Plant Diversity Taxonomy
-
Upload
raj1987kapoor9309 -
Category
Documents
-
view
1.691 -
download
2
description
Transcript of Plant Diversity Taxonomy
PlantDiversity
Ethnobotany
Forestry
Horticulture
Photosynthesis and Respiration
Plant Biotechnology
Plant Cells and Tissues
Plant Development
Plant Diversity
Plant Ecology
Plant Genetics
Plant Nutrition
PlantDiversity
J. Phil Gibson and terri r. Gibson
Series Editor William G. Hopkins
Professor Emeritus of Biologyuniversity of Western ontario
Plant DiversityCopyright 2007byInfobasePublishingAllrightsreserved.Nopartofthisbookmaybereproducedorutilizedinanyformorbyanymeans,electronicormechanical,includingphotocopying,recording,orbyanyinfor-mationstorageorretrievalsystems,withoutpermissioninwritingfromthepublisher.Forinformationcontact:ChelseaHouseAnimprintofInfobasePublishing132West31stStreetNewYorkNY10001
ISBN10:0-7910-8960-6ISBN13:978-0-7910-8960-6
Library of Congress Cataloging-in-Publication Data
Gibson,J.Phil.Plantdiversity/J.PhilGibsonandTerriR.Gibson.p.cm.—(Thegreenworld)Includesbibliographicalreferencesandindex.0-7910-8960-6(hardcover)1.Plantdiversity—Juvenileliterature.I.Gibson,TerriR.II.Title.III.Series.QK46.5.D58G532006580—dc222006023234
ChelseaHousebooksareavailableatspecialdiscountswhenpurchasedinbulkquantitiesforbusinesses,associations,institutions,orsalespromotions.PleasecallourSpecialSalesDepartmentinNewYorkat(212)967-8800or(800)322-8755.
YoucanfindChelseaHouseontheWorldWideWebathttp://www.chelseahouse.com
TextandcoverdesignbyKeithTregoandBenPetersonPrintedintheUnitedStatesofAmerica
BangIP10987654321
Thisbookisprintedonacid-freepaper.
AlllinksandWebaddresseswerecheckedandverifiedtobecorrectatthetimeofpub-lication.BecauseofthedynamicnatureoftheWeb,someaddressesandlinksmayhavechangedsincepublicationandmaynolongerbevalid.
Introduction vii
1 The Diversity of Plant Life 2
2 The History of Plant Systematics 18
3 Fungi and Algae 32
4 Seedless Nonvascular Plants The Bryophytes 50
5 Seedless Vascular Plants 62
6 Nonflowering Seed Plants The Gymnosperms 78
7 Flowering Plants The Angiosperms 94
Glossary 112
Bibliography 123 FurtherReading 125 Index 129
By William G. Hopkins
vii
“Have you thanked a green plant today?” reads a popular bumper sticker.Indeedweshouldthankgreenplantsforprovidingthefoodweeat,fiberfortheclothingwewear,woodforbuildingourhouses,andtheoxygenwebreathe.Withoutplants,humansandotheranimalssimplycouldnotexist.Psycholo-giststellusthatplantsalsoprovideasenseofwell-beingandpeaceofmind,whichiswhywepreserveforestedparksinourcities,surroundourhomeswithgardens,andinstallplantsandflowersinourhomesandworkplaces.Giftsofflowersarethemostpopularwaytoacknowledgeweddings,funerals,andothereventsofpassage. GardeningisoneofthefastestgrowinghobbiesinNorthAmericaandtheproductionofornamentalplantscontributesbillionsofdollarsannuallytotheeconomy.
Humanhistoryhasbeenstronglyinfluencedbyplants.Theriseofagri-cultureintheFertileCrescentofMesopotamiabroughtpreviouslyscatteredhunter-gathererstogetherintovillages.Eversince,theavailabilityoflandandwaterforcultivatingplantshasbeenamajorfactorindeterminingthelocationofhumansettlements.Worldexplorationanddiscoverywasdrivenbythesearchforherbsandspices.ThecultivationofNewWorldcrops—sugar,
viii introduction
cotton, and tobacco—was responsible for the introductionof slavery toAmerica,thehumanandsocialconsequencesofwhicharestillwithus.ThepushwestwardbyEnglishcolonistsintotherichlandsoftheOhioRivervalleyinthemid-1700swasdrivenbytheneedtoincreasecornproductionandwasafactorinprecipitatingtheFrenchandIndianWar.TheIrishpotatofaminein1847setinmotionawaveofmigration,mostlytoNorthAmerica,thatwouldreducethepopulationofIrelandbyhalfoverthenext50years.
Asayounguniversityinstructordirectingbiologytutorialsinaclassroomthatlookedoutoverawoodedarea,Iwouldaskeachgroupofstudentstolookoutthewindowandtellmewhattheysaw.Moreoftenthannotthequestionwouldbemetwithablank,questioninglook.Plantsaresomuchapartofourenvironmentandthefabricofoureverydaylivesthattheyrarelyregisterinourconsciousthought.Yettoday,facedwithdisappearingrainforests,explodingpopulationgrowth,urbansprawl,andconcernsaboutclimatechange,theproductivecapacityofglobalagriculturalandforestryecosystemsisputunder increasingpressure.Understandingplants isevenmoreessentialasweattempttobuildasustainableenvironmentforthefuture.
TheGreenWorldseriesopensdoorstotheworldofplants.Theseriesdescribeswhatplantsare,whatplantsdo,andwhereplants fit into theoverallschemeofthings.Plant Diversity introducesustotheseeminglyendlessvarietyinplantlife,fromthesmallestalgatothetallesttrees.Wealsolearnthesignificanceofplantdiversityinplanetaryecosystemsandwhy understanding and protecting this diversity is critical to our ownhealthandsurvival.
2
TheDiversityofPlantLife
It is my pleasure here to take Botany as my special study,which previously was the knowledge of a few plants;today however the abundance of material for choicehas made it the most extensive of all the sciences.
—Carolus Linnaeus (1707–1778)from the preface of Species Plantarum, 1753
Plants can be found nearly everywhere on Earth. They live in thecracksofNewYorkCitysidewalks.TheysurviveinthesandsoftheSahara.TheythriveinthejunglesoftheAmazonbasin.Theplantsthemselvesarenolessdiversethantheirsurround-ings, coming in all different colors, sizes, shapes, and scents(Figure1.1).Someplants,suchasannualbluegrass(Poa annua)andpoolsprite(Amphianthus pusillus),completetheirlifecycleinamatterofweeks,whereasindividualsofotherspecies,suchasbristleconepine(Pinus longaeva),canlivehundredsoreventhousandsofyears.Thesediversefeaturesnotonlyindicatetheability of plants to adapt to their environment, they also givecluestotheevolutionaryhistoryofplantsandinsightsintothehistoryoflifeonEarth.
TheVaLueoFPLanTDIVeRsITyKnowledgeandappreciationofplantdiversityhasalwaysplayedavitalroleinhumansurvival.Fortheearliesthunter-gatherers,itwasessential toknowwhichplantswereedibleandwhichwerenot.Carelesslyeatingthewrongkindofleaf,fruit,orseedcouldcausesicknessorevendeath.Asculturesdeveloped,earlyhumanslearnednotonlywhichplantstoeat,butalsowhichplants provided materials for housing, clothing, tools, anddyes. Plants such as sacred lotus (Nelumbo nucifera), peyote(Lophophora williamsii), and even cacao (Theobroma cacao), theplantfromwhichchocolateismade,wereusedinreligiousceremonies.Humansalsolearnedwhichplantshadmedicinalproperties.Individualswhoknewwhichplantstouse,wheretofindthem,andhowtopreparethemwereheldinhighregardasshamans,medicinemen,orhealerswhoseskillcouldmeanthedifferencebetweenlifeanddeathfortheirpeople.
Today,peoplestilldependonplantsfortheirsurvival.Plantsmakeupa significantportionof thedietof themore than6billionpeopleonthisplanet.Plantsprovidelumberandotherconstruction materials for housing. They provide fibers for
4
TheDiversityofPlantLife
5the diversity of Plant Life
Figure 1.1 Plants display a wide variety of forms. Photographed above are pine cones in a cluster (a), ferns found in the Bialowieza Forest in Poland (b), a cholla cactus (c), and a bouquet of pink tulips (d ).
a b
c d
6 Plant diversity
clothingandotheritems.Billionsofdollarsarespentannuallyonornamentalplantsandflowers.Eventhemodernpharmaceu-tical industrycontinuestodependonplants,withmorethan25% of prescription drugs containing compounds extractedfromplants.
Inadditiontobeingusefultohumans,plantdiversityisalsoimportant to the functioning of planetary ecological systems.Plantsdirectthecyclingofnutrientsbetweenthesoilandotherlivingorganisms.Throughphotosynthesis,plantsconvertenergyfromthesunintootherformsofenergythatnonphotosyntheticorganisms,suchashumansandotheranimals,canuse.Plantsregulate temperature, influenceprecipitationpatterns,providehabitatforotherorganisms,andperformmanyotheressentialecologicalprocesses.
Unfortunately, many human activities, particularly habitatdestruction,continuetohaveanegativeimpactonplantdiver-sity worldwide. Development of effective conservation strate-gies to protect botanical resources will depend greatly uponknowledgeofplantdiversityanditsecologicalimportance.Thus,appreciatingandunderstandingplantdiversityiscriticalforthesurvivalandqualityofalllifeonEarth.
EthnobotanyResearchers estimate that more than 80% of the world’s population still depends directly on plants for herbal medicines. Ethnobotanists are scientists who study the ways in which indigenous peoples use plants, par-ticularly for medicinal purposes. Many botanists, ethnobotanists, anthropol-ogists, and biochemists are currently working with native peoples around the world to learn about medicinal uses of different plants to preserve cultural traditions and knowledge. In the past, many medicines have been developed from plants used for healing purposes by tribal peoples.
7the diversity of Plant Life
ThesTuDyoFBIoLoGIcaLanDBoTanIcaLDIVeRsITyThebranchofbiologythatstudiesbiodiversity isknownassystem-
atics.Itismadeupofthreesubdisciplines:taxonomy,classification,andphylogeny.
Taxonomy is the process of naming individual plants orgroupsofplants.Aplantoftenhastwonames:acommon nameand a scientific name. Common names are given to plantsby the people who live near them. Sunflower, loblolly pine,cottonwood, and crabapple are examples of common namesfrequently used by scientists and nonscientists alike. Com-monnamesareofteneasytorememberandarefamiliartothegeneralpopulation.
Common names often describe some aspect of a plant’sphysicalappearance.Nameslikepitcherplant,cat’sclaw,fishon a line, or leafy elephant foot conjure images familiar toeveryone. Common names sometimes suggest a plant’s uses(broomstraw,matchweed,scouringrush)orwarnofitsdan-gers(stingingnettle,poisonivy,deathcamas).However,thisisnotalwaysthecase.Thenameshenbit,dogwood,andrattle-snakemasterarecolorful,butgivelittleinformationabouttheplantitself.
Aplantmayhavemorethanonecommonname.Forexample,waxgoldenweedandSpanishgoldbothrefertothesameplantspecies,Grindelia ciliata.Acommonnamemayrefertoseveralplantswithsimilarcharacteristics.Aquacatillo(“littleavocado”),forexample,isacommonnamethatidentifiesseveraldifferenttropicaltreespeciesthatproducesmallavocados.Consequently,commonnamescanbeaproblemforscientistsbecausetheyarenot necessarily specific to a single plant, there are no rules togoverntheirapplication,andtheyprovidelimitedinformationaboutaplantoritscharacteristics.
In the 1700s, a Swedish botanist named Carolus Linnaeus(1701–1778)reducedthepolynomial(manyname)systemtoabi-nomialsystem.Scientistscurrentlyusethisbinomial nomenclature
8 Plant diversity
(twoname)systemofscientificorLatinnamestoidentifyspe-cies.Forexample,thescientificnamefortheEuropeangrapeisVitis vinifera. Thefirstpartofthename(Vitis)isthegenus andthesecondpart(vinifera) is thespecies.Agenusnamecanbeusedalonetorefertoallmembersofagenus,butspeciesnamesareneverusedalone.
TheuseofscientificnamesforplantsisbaseduponasetofrulescalledtheInternational Code of Botanical Nomenclature (ICBN).AllnamesareinLatinorhavebeenLatinizedregardlessofaplant’slocation, its possible uses, or any associations with a particularculture. Latinwaschosenbecausethiswasthe languageoftheclassical works of botany and other sciences. Scientists aroundtheworldcancommunicatewithcertaintyaboutaspecificplant,regardlessofthelanguagetheythemselvesspeak.ThefollowingaresomeofthefundamentalICBNrules:
1. Aplantorgroupofplantscanhaveonlyonevalidname.
2. Thevalidnameforaspeciesistheonefirstpublishedclos-
esttothedateMay1,1753(thepublicationdateforCaro-
lusLinnaeus’bookSpecies Plantarum, whichisconsidered
thestartingpointformoderntaxonomy).
3. Anameisvalidifithasbeenpublishedinscientificlitera-
tureandcontainsacompletedescriptionoftheplantwrit-
teninLatin.
4. Avalidnameforaspeciesconsistsoftwoparts,agenusname
andaspeciesname.Thesetwopartsmaynotbethesame.
5. Agenusnamecanbeusedonlyonce,butaparticularspe-
ciesnamecanbeusedincombinationwithdifferentgenera.
Forexample,Carya glabra (pignuthickory)andRhus glabra
(smoothsumac)havethesamespeciesnameglabra(mean-
ing“withouthairs”),buttheyaretwodifferentspecies.
6. Thegenusandspeciesnamesareitalicizedorunderlined.
9the diversity of Plant Life 9
7. Thebotanicalrulesofnomenclatureareindependentof
therulesthatgovernnamingofotherorganisms.
TherearemanyotherrulesintheICBNthatgiveordertotheprocessofnaming.Botanistsfromaroundtheworldmeetevery
Families With two namesAlthough the ICBN states that there can be only one correct name for any group, there is an exception to this rule. Eight plant families have two cor-rect, accepted names. The modern names have endings consistent with the ICBN rules. The older names deviate from ICBN rules, but have been in use for so many years (centuries, in some instances) that many botanists still use them today.
Table1.1 Plant Families With Two Valid Scientific Names
ICBN name Older name Common name
Apiaceae Umbelliferae Parsleyfamily
Arecaceae Palmae Palmfamily
Asteraceae Compositae Sunflowerfamily
Brassicaceae Cruciferae Mustardfamily
Clusiaceae Guttiferae Garciniafamily
Fabaceae Leguminosae Beanfamily
Lamiaceae Labiatae Mintfamily
Poaceae Gramineae Grassfamily
10 Plant diversity
fiveyearsatthe International Botanical Congress todiscussrules,propose changes, and make sure that the ICBN is serving theneedsofthebotanicalcommunity.
Thesecondpartofsystematics,classification,istheprocessofgroupingnamedorganismsintoanorderedsystem.Smallergroups are placed together into progressively larger groups,likeaseriesofnestingboxes.Inmodernclassificationsystems,thelargest,mostinclusivegroupingisthekingdom (allplantsareintheKingdomPlantae).Plantsarethendividedintosuc-cessively smaller groups, the smallest, and least inclusive ofwhichisthespecies.Aspeciesisaparticularkindoforganismthattypicallycanreproducewithothermembersofthesame
Table1.2 International Code of Botanical Nomenclature Endings
Taxonomic Level ICBN ending Scientific name
Kingdom -ae Plantae
Division -phyta Embryophyta
Class -opsida Angiospermopsida
Subclass -idae Asteridae
Order -ales Asterales
Family -aceae Asteraceae
Genus Grindelia
Species Grindelia lanceolata
CommonName narrowleafgumweed
11the diversity of Plant Life
speciesandcanbedistinguishedfromotherspeciesbasedona number of different characteristics. Members of the samespeciesallshareanevolutionaryhistorydistinctfromthatofotherspecies.
The ICBN dictates specific endings for names at the dif-ferent levels of plant classification (Table 1.2). For example,allplantfamilynamesendwiththesuffix-aceae.Orders,theclassification level above family, end in -ales. Through thissystem,botanistscanquicklyrecognizethetaxonomiclevelofanyname.
Thefinalcomponentofsystematicsisthestudyofphylog-eny,theevolutionaryrelationshipamongorganisms.Throughthis type of research, systematists can show how organismsevolved,howdifferentorganismsare evolutionarily related tooneanother,andhowdifferentgroupshavedivergedanddif-ferentiatedfromoneanotherthroughouttime.Studiesofphy-logenyoftenresultintheconstructionofdendrograms,whicharebranchingdiagramsthatshowtheevolutionaryfamilytreeforagroup.
sIxKInGDomsoFLIFeAlthoughtherearedifferencesofopinion,mostbiologistsrecog-nizesixkingdoms:Bacteria, Archaea, Protista, Animalia, Fungi, and
taxonomic AbbreviationsSystematists have developed their own terms and shorthand abbreviations to refer to different taxonomic groupings. One of the most commonly used words is taxon (pl. taxa), which refers to a group at any classification level. Genus names can be used alone or followed by the abbreviations sp. or spp., which are abbreviations for the word species (sp. refers to a single species and spp. refers to multiple species).
12 Plant diversity
Plantae. Organismsareplacedintooneofthesekingdoms basedupontheirgeneticandcellularfeatures,aswellastheirmodesofobtainingnutrientsandenergy.
KingdomsEubacteriaandArchaeacontaindescendantsofthe oldest organisms on Earth. Members of these two king-domsareprokaryotic,meaningthattheircellslackanucleus andmembrane-bound organelles within them. Kingdom Bacteriais very diverse and contains a majority of the prokaryoticorganisms on Earth. This group includes the true bacteriaand cyanobacteria (blue-green algae). Kingdom Archaea isanotherdiversegroup.Manymembersofthiskingdomoftenlive inharshenvironments,suchashotspringsanddeepseathermalvents,inconditionssimilartothosefoundinEarth’searlyhistory.
The remaining four kingdoms are eukaryotic, meaning thattheircellscontainanucleusandmembrane-boundorganelles.Kingdom Protista contains many unicellular organisms andsimple multicellular organisms. Kingdom Protista containsorganismsthatsharesimilaritieswithanimals,fungi,andplants.Ofparticularimportancearethegreenalgae,whichplayedanimportantroleintheevolutionofplants.
KingdomsAnimaliaandFungicontainmulticellular,eukary-oticorganismsthatareheterotrophs; theymustconsumeotherorganisms to obtain the nutrition and energy they need tolive.Animalsingesttheorganismstheyfeeduponandsecreteenzymes that break down their food into simple molecules,whichareabsorbedbytissuesofthedigestivesystem.Incon-trast, fungi secrete enzymesonto their food source, and thenabsorb the digested food from the environment. Fungi werelongconsideredplants.Cellularandmoleculardata,however,haveshownconclusivelythatfungiarenotplantsandshouldbeplacedinaseparatekingdom.Interestingly,geneticdatahaveshown that fungiareactuallymoreclosely related toanimalsthantoplants.
13the diversity of Plant Life
Kingdom Plantae contains organisms that are autotrophs,
which means that they are capable of producing their ownenergy.Botanistshaveidentifiedmorethan300,000differentspecies of plants; there may be as many as 500,000 differentplant species on Earth. Plants are divided into four majorgroups: bryophytes, seedless vascular plants, gymnosperms, andangiosperms.
WhaTIsaPLanT?Likeall living things,plantsarecomposedofcells,useenergyandnutrientsintheirmetabolism,andhaveevolvedavarietyofadaptationsthathelpthemsurviveintheirenvironment.Plantsalso reproduce and interact with other living things. Severaluniquefeatures,however,makeitpossibletogrouptheseorgan-ismsintotheirownkingdom.
Avastmajorityofplantsarephotoautotrophs. Theyconductthebiochemicalprocessofphotosynthesis in structurescalled
chloroplasts (Figure1.2). Throughphotosynthesis,plants convertenergyinsunlightintochemicalformsofenergy,suchassugarsandstarch,thattheycanthenusetomeettheirownneedsandprovideenergytootherlivingthings.Plantsconductphotosyn-thesisusinguniquecombinationsofdifferentpigments,suchaschlorophyll a,chlorophyll b, and carotenoids. Somephotosyntheticbacteriacontainchlorophyllb,butonlyplantsandgreenalgaecontain theotherphotosyntheticpigments. It isworthnotingthatthereareparasiticplants,suchasdwarfmistletoes(Arceu-thobium) and Indian pipe (Monotropa uniflora), that do notproducephotosyntheticpigmentsandarenotphotosynthetic;despite this, theirbiologyandothertraitsclearly indicate thattheyareplants.
Theplantcellwallisanotheruniquefeatureoftheseorgan-isms. Plant cells are surrounded by a wall made of complexcarbohydrates,suchascelluloseorlignin,whichprovidesrigidityandstructuralsupportfortheplantbody.
14 Plant diversity
Anotherdefiningtraitofplantsisthatthestructuresinwhichgametes(eggsandsperm)areproducedaresurroundedbyalayerof cells called the sterile jacket, which protects the developinggametes.Furthermore,theplanteggisnotcapableofmovementandthusremainsinfemalegametophytetissues.
Figure 1.2 Plant cells are made out of many components, including a nucleus, cell wall, and chloroplasts.
15the diversity of Plant Life
TheaLTeRnaTIonoFGeneRaTIons
Alllivingthingshavealifecycle.Themostfamiliarlifecycletomostpeopleisthatofanimals,inwhichsingle-celledgam-etes unite during sexual reproduction to form a multicellularzygote that grows and develops into a mature adult. Gam-etes are haploid (contain one complete set of chromosomes).Zygotesandadultsarediploid (contain twocomplete setsofchromosomes).Haploidcellsareproducedwhendiploidcellsundergotheprocessofmeiosis, dividingtwicetoproducefourhaploidcells.Mitosisis asimilarprocess, butinsteadofhalv-ingthegeneticmaterialinthecell,itproducestwoidenticalcellswiththesameamountofgeneticmaterialastheoriginalparentcell.
Plants go through haploid and diploid phases in the lifecycle.Thisunique typeof lifecycle is called thealternation of
generations because during sexual reproduction there is analternationbetweenamulticellularhaploidgenerationcalledthe gametophyte and a multicellular diploid generation calledthe sporophyte (Figure 1.3). The gametophyte is a plant thatproduces gametes. Through fertilization, the egg and spermunite to form a zygote that becomes the diploid sporophyte.Thesporophyteisaplantthatproducesspores.Thesporophytegrowsthroughmitosis.Eventually,specialcellsinitsreproduc-tivetissues(spore mother cells) undergomeiosistoformhaploidspores.Thesporesgerminatetoformthegametophyte,andthecyclerepeatsitself.
Thealternationofgenerations is important in thestudyofplant diversity because the four major groups of plants differwith regard to which generation, gametophyte or sporophyte,dominatesthelifecycle.Inbryophytes,forexample,thegameto-phyteisthedominantgeneration,whereasthesporophyteisthedominantgenerationinangiosperms.
16 Plant diversity
summaRy
PlantsareanimportantcomponentoflifeonEarth.Theypro-videavarietyofecologicalservicesrangingfromtheproductionoffoodthroughphotosynthesistoprovidinghabitatsforotherlivingthings.Plantsalsoprovideamultitudeofnaturalresourcesforhumansandhaveperformedimportantrolesintheevolutionofhumansandthegrowthofhumanculturesandpopulations.
Figure 1.3 Plants alternate between sporophyte and gametophyte phases. Sporophytes undergo meiosis to form spores, which initiates the gametophyte phase. Gametophytes have half the number of chro-mosomes as sporophytes. Male and female gametophytes, or gametes, combine during fertilization. The result of fertilization is the formation of a zygote.
17the diversity of Plant Life
Throughsystematics,botanistsidentifyandorganizethediver-sityofplantlifenotonlytocataloguebotanicaldiversity,butalsotounderstanditsoriginsandevolutionaryhistory.
1818
ThehistoryofPlantsystematics
ThehistoryofPlantsystematics
The botanist is he who can affix similar names tosimilar vegetables, and different names to different ones,
so as to be intelligible to every one—Carolus Linnaeus
20 Plant diversity
20
The earliest efforts to categorize plants were based on their usefulness to humans. Ancient texts and records describingmedicinal,agricultural,andotherusesofplantshavesurvivedfromculturesaroundtheworld.Oneoftheoldestsuchbookswaswrittenmorethan4,500yearsagobyEmperorChi'enNungofChina.Onethousandyearslater,anunknownauthorwrotetheEberspapyrus,ascrollthatdescribedthepharmacologicalusesofplantsfoundinancientEgypt.
Morethan2,300yearsago,theGreeknaturalistTheophrastus wroteaboutthecultivationandusesofvariousplants,organizingthemintogroupsbasedoncharacteristicssuchastheirgrowthform (herb, tree, or shrub), fruit, and leaves. He gathered muchoftheinformationforhisbookHistoria Plantarum (HistoryofPlants)bystudyingthegardensofAthens.Heeventuallyestab-lishedthefirstknownbotanicalgarden.
RomannaturalistPlinytheElder(a.d.23–79)describedthehorticulturalandmedicinalusesofmanyplantsinhisbookHis-toria Naturalis (NaturalHistory).Dioscorides(circaa.d. 40–90),aGreekphysicianinNero’sarmy,wroteDe Materia Medica (TheMaterialofMedicine),abookthatclassifiedanddescribedmorethan600plants.NotonlydidDe Materia Medicacontainwrittendescriptions,itwasalsothefirstbotanybooktoincludeillustra-tions.Thisbookwasoneof theprimarymedicalreferences inEuropeuntilthe1600s.
OnethousandyearsafterPlinyandDioscorides,aChinesephy-siciannamedTangShen-weipublishedCheng Lei Pen Ts’ao (TheMaterialsofMedicineArrangedAccordingtoPattern).Firstpub-lishedin1108,thisclassicworkofEasternmedicinewentthrough12editionsandwaseventranslatedandpublishedinJapanin1625.
TheReBIRThoFBoTanyIn Europe, botany—like other sciences—lay mostly dormantuntil the Renaissance. The renewed interest at this time coin-cidedwiththeinventionoftheprintingpress,whichusheredintheso-calledAgeofHerbals.Forthefirsttime,leadingGerman
ThehistoryofPlantsystematics
21the History of Plant Systematics
botanists,suchasOttoBrunfels,HieronymusBock,andLeonartFuchs,wereabletopublishandwidelydistributebooksthathaddescriptionsandpicturesofplants(Figure2.1).
The firstuniversities inUpper ItalyandEuropeestablishedbotanicalgardenstostudyliveplants.LucaGhini(1490–1556),working at the University of Pisa, invented the process of
Figure 2.1 Herbals are books that describe the many characteristics of plants used in herbal medicines. This illustration of a peony is from an herbal published in 1613.
22 Plant diversity
collecting,pressing,anddryingplantstocreatethefirstherbarium,alibraryofpreservedplantmaterials.Theherbariumestablishedin1532byGhini’sstudentGherhardsCibo(1512–1597)istheoldeststillinexistence.
Althoughresearcherscontinuedtofocusonthemedicinalusesofplants,botanistsof theseventeenthcenturybeganto investi-gateotherareas,aswell.Theirdiscoveriesledtothedevelopmentof thefirstclassificationsystemsbasedonfeaturesof theplantsratherthantheiruses.Naturalists,suchasJohnRay(1628–1705)andPierreMagnol(1638–1715),describedandnamednumerousEuropeanandAsianspecies,genera,andfamilies.Thesebotanistsandothersbegantoclarifyconceptsaboutplantfamiliesandgen-erathatwouldbecomethefoundationofmodernsystematics.
caRoLusLInnaeusBytheeighteenthcentury,botanistshadcollected,stored,stud-ied,andclassifiedagreatdealofplantmaterialfromaroundtheworld.Therewasnostandardizedsystemorconsensus,however,abouthowtonameaplant—oranyotherkindoforganism,forthatmatter.This ledtoapolynomialsystemthatwascumber-someandimpractical.Forexample,thefullnameforoneplantspecies was Serratula foliis ovato-oblingis accuminatus serratis,
What is an Herbarium?An herbarium is a library of pressed and dried plants. In the herbarium, dried whole plants or parts of plants are mounted on pieces of paper called herbarium sheets. Each sheet has a label that identifies the plant and tells where and when the specimen was collected and by whom. Many professional systematists work at herbaria associated with botanical gardens, colleges, or universities. Specimens collected by Linnaeus are in herbarium collections around the world.
23the History of Plant Systematics
floribus corymbosis, calcybus subrotundis. When the binomialsystem(seeChapter1)wasintroducedbyCarolusLinnaeus,thiswasshortenedtoSerratula glauca.
InSpecies Plantarum,publishedMay1,1753,Linnaeusgavebinomialnamestomorethan7,300species(Figure2.2).Althoughhe was not the first person to consider a simplified binomialsystem, Linnaeus was the first to develop and consistently useaworkablenamingsystem—onethathasbeeninuseformorethan200years.
naTuRaLcLassIFIcaTIonsysTemsanDeVoLuTIonAlthough his binomial system was successful, Linnaeus’s clas-sification system was not widely accepted. Linnaeus catego-rizedplantsbasedonthenumberandarrangementofstamens,and then subdivided them using other floral traits. This arbi-traryapproachproducedanartificial classification system,whichgroupedunrelatedspeciestogether.
ContemporariesofLinnaeus,suchasMichelAdanson(1727–1806)andAntoineLaurentdeJussieu(1748–1836),preferredtouseamultitudeofdifferentfeatures(forexample,flowers,fruits,andleaves)togroupplantsbasedonoverallsimilarity.Usingthisapproach, De Jussieu described more than 100 plant families,manyofwhichthatarestillrecognizedtoday.
Famous Botanists rememberedScientists often recognize individuals who have made major contributions to the field of botany by naming plants after them. The genus Magnolia is named after the botanist Pierre Magnol, whose work developed the concept of plant families. The genus Dioscorea (yams) is named in honor of the Greek botanist Dioscorides. Several paintings show Linnaeus wearing or holding a small cluster of Linnaea flowers, a genus that was named after him.
24 Plant diversity
Figure 2.2 Carolus Linnaeus is known for his contributions to modern taxonomy. This famous picture of Linnaeus in Lapland dress shows him holding a cluster of flowers named after him, Linnaea borealis.
25the History of Plant Systematics
De Jussieu was one of the first botanists to group relatedspecies and families together. This approach produced a natu-
ral classification system that reflectedevolutionaryrelationshipsamongplants.Thegoalofproducingnaturalclassificationswasfurtherenhancedwiththepublicationof The Origin of Species in1859. In this groundbreakingbook,CharlesDarwin describedhowspeciesevolveandhowadaptationsandothertraitsspreadthroughtheprocessofnatural selection.Naturalselectionoccurswhenorganismshavetraitsthathelpthemsurvivebetterorpro-ducemoreoffspringthanthosethatlackthosetraits.Throughgreatersurvivalandoffspringproduction,organismswithadap-tivetraitsleavemoredescendants,andtheadaptationbecomesmoreprevalentinfuturegenerations.Withhistheoryofevolu-tion,Darwinshowedthatthediversityoflifecouldbeinterpretedasafamilytree,orgenealogy,thatrevealshowtaxahavechangedthroughouttime.
eVoLuTIon-BaseDcLassIFIcaTIonsAsthetheoryofevolutionspread,botanistsquicklydevelopedevolution-basedclassifications.Prominentbotanists,suchasA.P.deCandolle(1778–1873)inSweden;GeorgeBentham(1800–1884)andSir JosephHooker(1817–1911) inEngland;AugustWilhelm Eichler (1839–1887), Adolf Engler (1844–1930), andKarlPrantl(1849–1893)inGermany;andAsaGray(1810–1888)andCharlesBessey(1845–1915)intheUnitedStates,developedclassificationsystemsinwhichtheyconsideredtheevolutionaryhistory of specific traits. Some general rules they followed indevelopingevolution-basedclassificationsincluded:
• Flowerswithmanyparts(forexample,manystamensor
carpels)arelessadvancedthanflowerswithfewerparts.
• Plantswithwoodystemsaremoreprimitivethanherba-
ceousplants.
26 Plant diversity
• Specieswithflowerscontainingmaleandfemalestructures
arelessadvancedthanspecieswithflowersthatcontainonly
maleoronlyfemaleparts.
Thisnewevolutionaryperspectivegaverisetomodernclas-sificationsthatshowthephylogenyorevolutionaryhistoryandrelationships among organisms in a lineage. Researchers con-tinuetodevelopclassificationsthatdisplaytheevolutionofdif-ferentplantgroups.
moDeRncLassIFIcaTIonsArthurCronquist(1919–1992),LedyardStebbins(1906–2000),andRobertThorne(b.1920)oftheUnitedStates;ArmenTakhta-jan (b. 1910) of the former Soviet Union; and Rolf Dahlgren(1932–1987)ofDenmarkproducedmajorclassificationsystemsforangiospermsthatinfluencedmodernthinkingonfloweringplantevolution.Currently,systematistsworkinginmanydifferentlaboratoriesandherbariatakepartininternationalcollaborativeefforts,suchastheAngiospermPhylogenyGroupandtheTreeofLifeProject.ThesegroupsseektoclarifyourunderstandingofthehistoryoflifeonEarthbyinvestigatinglarge-scalepatternsofplantevolution.
cLaDIsTIcsanDconsTRucTInGPhyLoGenIesSystematistsconstructphylogeniesusinganapproachcalledcla-
distics,atermthatcomesfromtheGreekwordforbranch,klados.
the Meaning of theoryEvolution is sometimes discredited as a theory and not a fact. Scientists use the term theory to refer to a collection of unifying principles that explain proven facts and observations. Thus, the theory of evolution is not a guess, but a well-supported scientific explanation for the diversity of life.
27the History of Plant Systematics
Theobjectiveofcladisticsistoproduceanaturalclassificationinwhicheverydescendantofasingleancestorisplacedonthesamebranch (clade)of adendrogram.Whenallof thedescendentsofacommonancestorareplacedinthesameclade,itiscalledamonophyletic group.By identifyingmonophyleticgroups, sys-tematistscandeterminehowspecifictraitsinalineageevolvedthroughouttime.
Foracladisticstudy,systematistsfirstdeterminewhichchar-acteristicsareprimitive(ancestral)andthenwhichareadvanced.For example, Table 2.1 shows five different traits in the fourmajor groups of plants and algae. The presence of a particu-lar trait is amore evolutionarily advancedcondition than theabsenceofa trait.Forexample,plantswithoutvascular tissue
Table2.1 Comparison of Traits Between Algae and Major Green Plant Groups
Seedless vascular Gymno- Angio- Trait Algae Bryophytes plants sperms sperms
Presence of chlorophylls yes yes yes yes yes a and b
Sterile jacket layer around no yes yes yes yes antheridia and archegonia
Vascular tissue no no yes yes yes
Seeds no no no yes yes
Flowers no no no no yes
28 Plant diversity
(xylemandphloem)appearinthefossilrecordbeforeplantswithvasculartissue.Therefore,theabsenceofvasculartissueinagroupofplantsisamoreprimitiveconditionthanthepresenceofvascu-lartissue.Cladistsusethepatternsofhowadvancedtraitsarisetodetermineevolutionaryrelationshipsamongmembersofalineage.
The data in Table 2.1 can be used to produce a cladogram(Figure2.3)thatdescribesthephylogenyforthemajorgroups
Figure 2.3 The above cladogram shows the relationship among major plant groups.
29the History of Plant Systematics
ofplants.Thiscladogramshowsthatallplantssharedadistantcommon ancestor with algae. Bryophytes are the oldest plantlineage,followedbytheseedlessvascularplants,gymnosperms,andultimatelytheangiosperms.Systematistsusethebranchingpatternsofacladogramtodeveloptheirclassifications.
TheDaTasysTemaTIsTsuseSystematicshasbeenreferredtoasthefieldofsciencewithnodataofitsown.Insomeways,thatiscorrect.Unlikethephysiolo-gistwhocollectsdataonthemetabolicrates,cycles,andprocessesincells,thegeneticistwhocollectsdataonthesequenceofgenesonachromosome,ortheecologistwhocollectsdataonthesizeanddistributionofpopulations,systematistsdonotcollectanyformofdata thatonecouldspecifically identifyassystematicsdata.Instead,theyusethetechniquesofotherscientificfieldstocollectdatathattheycanthenusetodevelopaclassification.
Intheearlystagesofsystematics,botanistsdependedheavilyonmorphology(theoutwardstructuralappearanceofaplant).Traitssuchasleafshape,fruittype,ornumberofpartsinaflowerareeasytoobserveandcompareamonglivingandfossilplants.Withtheinventionofthemicroscope,botaniststurnedtoanatomy (theinternalcellularstructureofaplant)todevelopclassifications.
Botanical resourcesThere are many resources available for individuals who want to explore the botanical diversity around them. One good resource is a field guide. These books often have pictures and descriptions that make it easy for budding botanists to learn the common plants of an area. More advanced students may require a flora, which typically contains an extensive listing of species that occur in an area. Field guides and floras typically contain dichotomous keys, which help users identify plants by leading them through a series of paired questions.
30 Plant diversity
Figure 2.4 DNA sequencing gels are used by modern-day taxonomists to collect genetic data. Each band represents a single fragment of DNA known as a nucleotide. There are four types of nucleotides, abbreviated G (guanine), T (thymine), A (adenine), and C (cytosine).
31the History of Plant Systematics
The field of systematics is constantly changing as differenttechnologicaladvancesarise.Asinstrumentsandtechniquesforanalysisofplantchemicalextractsimprovedinthe1940s,system-atistsbegantocollectchemicaldatafortheirstudies.Inthe1990s,there were tremendous advances in the ability to extract andsequenceDNAfromplantsandimprovedcomputingabilitytoanalyzedatafromDNA(Figure2.4).Systematistsrapidlyincor-poratedthesenewtechniquesintotheiranalyses.Newtechniquescombinenewdatawithearlierformsofdatatofurtherrefinetheunderstandingofplantevolution.
Thereisevencontinueddiscussionamongplantsystematistsabouthoworganismsshouldbenamedandclassified.Recently,systematistsproposedmovingaway fromtheLinnaeansystemtoward a system called the Phylocode, which has no hierarchi-calrankings,suchasfamilyororder.Instead,itonlyrecognizesclades.Although there is skepticismabout thevalueof suchasystemandhowitwouldaffectthestudyofplantdiversityoverall,itdoesillustratehowbotanistscontinuetothinkaboutnaming,classifying,andinterpretingthehistoryofplantdiversity.
summaRyThroughouthumanhistory,individualshaveworkedtodescribeandorganizethediversityofplantlifeonEarth.Earlyartificialclassificationswerebasedprimarilyuponaplant’susefulnesstohumans.Throughouttime,systematistsdevelopednaturalclas-sificationsthatpresenttheevolutionaryhistoryofplantgroups.Linnaeusisoneofthebest-knownnamesinthehistoryofbotany,butmanydifferentindividualshavecontributedandcontinuetoplayasignificantpartinthisfieldofstudy.
32
Fungiandalgae
Did you hear about the fungus and the alga? They took a lichen to each other.
—Unknown
Although there are many beneficial species of fungi, people often fearthembecauseoftheirtoxinsandotherundesirablefeatures.Forexample,fungicalledmoldscauseallergiesandotherrespi-ratory illnesses. Other species produce strong hallucinogeniccompoundsthathavearangeofeffectsonthenervoussystem.Otherfungi,however,producechemicalsthatbenefithumans.TheimportantantibioticpenicillinisderivedfromthefungusPenicillium chrysogenum. As a further example, the yeast Sac-charomyces cerevisiae isaninvaluablefungususedtomakebread,beer,andwine.
Like so many of the fungi, algae too are often overlookedor unwanted. A thick growth of algae can pollute ponds andrender water undrinkable (Figure 3.1). Fish tanks often needtobecleanedtoremovealgalgrowth.Otheralgae,however,arevaluedfortheirusefulness.NoriandsealettuceareusedinAsiancooking. Carrageenan, a product derived from algae, is usedin ice cream, sauces, shampoos, cosmetics, air fresheners, andmanyotherproducts.Algaearealsoof immeasurableecologi-calimportanceinoceans,lakes,andstreams,wheretheyarethefoundationofthefoodchain.
At different times, fungi and algae have been classified asplants.Althoughthesegroupsdosharesimilaritieswithplants,fungi differ enough to warrant their own kingdom. Whetheralgaeshouldbeplacedinadifferentkingdom,however,dependsonwhichalgaisbeingconsidered.
Fungiandalgaehaveplayedvitalrolesinplantevolution.Anancestralalgalspeciesestablisheditselfintheterrestrialenviron-mentandgaverisetoallplants.Thisinvasionoflandwasmadepossiblethroughinteractionsbetweenplantsandfungi.Becauseearlyplantshadnoroots,plantsandfungiformedrelationshipsinwhichfungiprovidedplantsnutrientsfromthesoil.Amajor-ityofplantstodaystillformtheseimportantsymbioticrelation-shipswithfungi.
34
Fungiandalgae
35Fungi and Algae
FunGIMycology (fromtheGreekwordforfungus,mykes)isthestudyof fungi.Likeplants, fungiaremulticellulareukaryoteswhosecellsproduceacellwall.Fungicellwalls,however,arecomposedpredominantlyofchitin(asubstancealsofoundintheexternalskeletons and shells of insects, crustaceans, and other relatedanimals).
Fungiarecomposedofmanysmallthreadlikestrandsofcellscalledhyphae. The collection of hyphae that make the fungal
Figure 3.1 Excessive growth of algae can reduce the quality of freshwater lakes and ponds.
36 Plant diversity
body is called a mycelium. Fungi range in size from unicellu-lar yeasts to the immensely large individuals that cover greatareasinforests. Fungiareheterotrophsthatfeedonlivinganddeadorganisms.Theyobtainenergyandnutrientsbygrowinghyphae through the body of their food source and secretingenzymesthatbreakitdownintosmaller,simpler,organicmol-ecules,whicharethenabsorbed.Thismethodof feedingmakesfungi,alongwithbacteria,extremelyimportantasdecompos-ersthatclearorganicwastefromtheenvironmentandreturnnutrientstothesoil.
BasIcFunGaLLIFecycLeMany fungi reproduce asexually as well as sexually. In asexual
reproduction,sporesareformedinaspecializedstructurecalledasporangium (plural:sporangia)andthenreleasedtotheenviron-ment.Fungidonothavemaleandfemaleindividuals.Instead,sexualreproductionoccursbetweengeneticallydifferentmating
types.Forsexualreproduction,haploidmyceliaofdifferentmat-ingtypescomeintocontactwithoneanother,allowingcellsfromdifferenthyphaetofuse.Althoughthecellscombine,theirnucleicanremainseparatewithinthemandgrowasamyceliumcom-posedofthesedikaryoticcells.Whethertheseparatenucleifuse
the Humongous FungusWhile several plants are candidates for the title of “largest or oldest organ-ism on Earth,” the fungi kingdom also has individuals of tremendous size and age. The honey mushroom (Armillaria ostoyae) is a fungus that attacks the roots of conifers. The mycelium of one individual in southwest Wash-ington State was measured to cover 1,500 acres (approximately 2.5 square miles). Another, growing in eastern Oregon, covers 2,200 acres (3.4 square miles) and may be more than 2,400 years old.
37Fungi and Algae
immediatelytoformazygoteorcontinuetogrowasadikaryoticmyceliumuntilformingazygoteatalatertimeisadistinguishingfeatureamongdifferenttypesoffungi.
majoRFunGaLGRouPsMycologistshaveidentifiedandnamedmorethan50,000spe-ciesoffungi(Table3.1andFigure3.2)andhaveestimatedthatthetotalnumbermaybecloseto1.5million.Fungiareamono-phyleticgroup,buttheirclassificationhasbeenchallenging.Forexample,recentadvancesinthecollectionandanalysisofgeneticandothermoleculardatahaveallowedmycologiststodeterminethatthewatermolds(Oomycota)andslimemolds(Dictyoste-liomycotaandMyxomycota),whichhadlongbeenclassifiedasfungi,arenotfungiatall,butareinfactprotists.
Presently,mycologistsrecognizefivemajorphyla(equivalenttothebotanicallevelofdivision)offungi:chytrids(Chytrido-mycota), zygomycetes (Zygomycota), arbuscular mycorrhizal
Table3.1 Major Groups of Fungi
Group Common name Estimated species
Chytridomycota chytrids 1,000
Zygomycota zygomycetes 1,100
Glomeromycota arbuscularmycorrhizal 157
fungi
Ascomycota sacfungi 32,00
Basidiomycota clubfungi 26,000
38 Plant diversity
Figure 3.2 Fungi display a wide range of growth forms. In the above pho-tographs; two fly agaric mushrooms (a), cultured Beauveria bassiana (b), a bunch of mushrooms at the base of a withered plum tree (c), and the fungal pathogen Candida albicans, as seen under a microscope (d).
a b
c d
39Fungi and Algae
fungi (Glomeromycota), club fungi (Basidiomycota), and sacfungi (Ascomycota).Currentperspectiveson fungal evolutionindicatethatthechytridsandzygomycetesaretheoldestlineages(Figure3.3).Arbuscularmycorrhizalfungi,clubfungi,andsacfungiaremoreadvancedgroups.Clubfungiandsacfungiarecloselyrelatedandencompass95%ofallknownfungi.
Figure 3.3 This cladogram shows the phylogeny of major fungal groups.
40 Plant diversity
ChytridsChytridomycotaaretheoldestgroupoffungi.Theyliveprimar-ilyinornearwaterandaretheonlygroupoffungitoproducesporesandgameteswithflagella(singularflagellum),atail-likestructure that gives cells the ability to move. The presence offlagellainthislineageprovidesevidencethat,likeallotherorgan-isms,fungifirstevolvedintheseas.
Thechytridlifecycleissimple.Haploidsporesgerminateandformahaploidmycelium,whichreleasesmaleandfemalegam-etes.Thegametesfuseandimmediatelyformadiploidmyceliumthateventuallyformsasporangium.Cellsundergomeiosisinthesporangiumandreleasethehaploidspores.
Chytrids are important decomposers of plant material inmanyaquaticsystems.AchytridcalledBatrachochytrium den-drobatidisiscurrentlyattackingamphibianpopulationsworld-wide and may be responsible for the extinction of severalamphibianspecies.
ZygomycetesZygomycotaarearelativelysmallfungalgroupofabout1,100species.Afrequentlyencounteredzygomyceteisthecommonbread mold in the genus Rhizopus. In asexual reproduction,sporangia form on the tips of upright hyphae and releasenumerousspores.Duringsexualreproduction,fusedhyphaefromdifferentmatingtypesformazygospore(thesmallblackdotsseeninmoldybread).Azygosporeishighlyresilienttoenvironmentalconditionsandcanremaindormantuntilenvi-ronmental conditions cue favorable conditions for releasingspores.
Arbuscular Mycorrhizal FungiMycologists recently moved a group out of Zygomycota andclassified themas anewphylum,Glomeromycota.Their com-monname,arbuscularmycorrhizalfungi,highlightsthisgroup’s
41Fungi and Algae
important features. Mycorrhizae (which literally means“fungalroot”)arefungithatgrowonahostplant’sroots.Theplantpro-vides the funguswithacarbohydrateenergysource. Inreturn,thefungusprovidestheplantwithnutrientsfromthesoil.Thistypeofplant-fungusmutualismoccursinthemajorityofplantsonEarth.Arbuscules arespecializedstructuresformedbythefungusinsidetheplantcellthatenabletheplantandfungustoexchangenutrients.Thearbuscularmycorrhizalfungiaretheonlygroupofmycorrhizalfungithatformthesespecializedstructures.
Arbuscularmycorrhizalfungiareobligatemutualists,mean-ingthattheyareunabletolivewithouttheirplanthost.Mycol-ogists cannot even culture them in the laboratory. Sexualreproduction has never been observed in any member of thisgroup.
Sac FungiAscomycotaisalargegroupthatincludesmorethanhalfofallknownfungi.Theircommonname(sacfungi)comesfromthesac-shaped structure called an ascus (plural: asci) that formsduring sexual reproduction.Asci form on the edge of a largereproductivestructurecalledanascocarp thatischaracteristicofthesefungi.Duringsexualreproduction,differentmatingstrains
chestnut BlightAmerican chestnut (Castanea dentata) once accounted for 25% of the trees in the eastern forests of North America. Then, in the early 1900s, a disease known as chestnut blight was accidentally introduced into North America from China or Japan. The disease, caused by the fungus Cryphonectria para-sitica, attacked native chestnut trees and by 1940 had driven the species to the brink of extinction. In April 2006, however, a small group of chestnuts was discovered near Warm Springs, Georgia. Scientists believe that these trees survived because the site is too dry for the fungus.
42 Plant diversity
fuse,formingadikaryoticmycelium.Themyceliumthenformsanascocarpwiththeascionit.Insidetheasci,thenucleifuse,andthenimmediatelyundergomeiosistoformhaploidspores,whichgerminatetoestablishanewmycelium.
Ascomycetes are important decomposers in many ecosys-tems. The sac fungi also include many species that cause dis-easeinawidevarietyofcropsandwildspecies.Therearealsomanybeneficialascomycetes.ThegenusPenicillium includesthesourceofpenicillin(Penicillium chrysogenum),thebluecheeses(Penicillium roqueforti and Penicillium camembertii), and theyeast used in brewing and baking (Saccharomyces cerevisiae).Morels(Morchella)andtruffles(Tuber)areconsidereddelicaciesbysomeindividuals.
Club FungiThe mushrooms, toadstools, and puffballs common to forestsandfrontyardsaremembersoftheBasidiomycota.Thenameclub fungireferstotheclub-shapedsporangium,calledabasid-
ium (plural:basidia), formedduringsexualreproduction.Asinothergroupsoffungi,thesexualreproductionofbasidiomycetesbeginswiththejoiningofdissimilarmatingstrains.Theresult-ingdikaryoticmyceliumformsareproductivestructurecalledabasidiocarp (thefamiliarmushroom).Thegillsontheunder-surfaceofthebasidiocarpformnumerousbasidia inwhichthedikaryoticnucleifusetoformazygote.Thesingle-celledzygotethenundergoesmeiosistoformhaploidsporesthatarereleasedtogerminateandproducenewmycelia.Thezygoteistheonlydiploidcellintheentirebasidiomycetelifecycle.
Clubfungiareadiversegroupthathasmanydifferentprop-erties and uses. The white button or portabella mushroom(Agaricus bisporus),oystermushroom(Pleurotus ostreatus), andshiitakemushroom(Lentinula edodes) areeatenonsalads,piz-zas,andmanyotherdishes.Amanita bisporigera, Amanita virosa,andAmanita verna areknownasdeathangelfungi becauseof
43Fungi and Algae
theirlethaltoxinsandalmostpurewhitecolor.Flyagaric(Ama-nita muscaria)andpsilocybinmushrooms(Psilocybe cubensis)produce hallucinogenic compounds that have been used byshamans—a religious specialist or medicine man—in ancientcultures and religions worldwide. Shelf fungi are importantdecomposers of wood and other plant materials. Club fungicalled rusts and smuts are serious plant pathogens that causebillionsofdollarsincropdamageannually(Figure3.4).
Figure 3.4 Smut, a fungus that causes plant disease, attacks many cereal crops. Above, mature smut galls are exposed on an ear of corn.
44 Plant diversity
aLGaePhycology, thestudyofalgae,coversawiderangeofphotosyn-thetic organisms—from minute diatoms, whose shells displayintricate patterns and structural variations, to the enormouskelps thatgrow in thecoldoceansofnorthern latitudes.Thisdiversityhasallowedalgaetosucceedinawiderangeofhabi-tats.Algaeliveinsoil,sand,andonthebarksoftrees.Someevengrowinsnow.Manyliveintheoceans,wheretheyformthebaseof marine food webs. Others perform the same ecological rolein freshwaterecosystems.Somegreenalgaehaveevenevolvedunusualassociationswithotherorganisms.
Green algaeareofparticularimportancebecausetheyarethegroupfromwhichlandplantsevolved.Twoothergroups—thered algae (division Rhodophyta)andthebrown algae (familyPha-eophyceae)—arealso includedhere,however,becauseof theirimportanceandfamiliaritytohumans.
Green AlgaeGreenalgaeareancient;theiroriginscanbetracedbackmorethan900millionyears.Throughoutthecourseoftime,theoneoriginalunicellularspeciesdiversifiedtoformotherunicellularspecies, as well as larger, more complex, multicellular growthforms.
GreenalgaLifecycleGreenalgallifecyclesincludesexualandasexualreproduction.Inunicellularalgae,asexual reproductionvia spore formationorcelldivisioniscommon.Sexualreproductioninunicellulargreenalga involves flagellated,haploid individualsofdifferentmating types simply coming together and fusing nuclei. Theresultingdiploidzygospore undergoesmeiosisandreleaseshap-loid unicellular individuals. Cells are also typically haploid inmulticellulargreenalgae.Duringsexual reproduction inmul-ticellular species, some of the haploid cells release flagellated,
45Fungi and Algae
unicellulargametes,which join inaprocess similar to thatofunicellular algae. The resulting single-celled zygote undergoesmeiosisandreleaseshaploidsporesthatgrowtobecomemulti-cellularindividuals.
GreenalgaeLineagesareRelatedtoLandPlantsGreen algae are a large group with more than 17,000 species.Therearethreemajorgroupswithinthegreenalgae:prasino-phytes,chlorophytes,andthecharophytes.Prasinophytesareadiversegroupofunicellularmarinealgae.Thisgroupincludesseveralseparatelineagesand,thus,isnotamonophyleticgroup.Prasinophytesareimportantbecausetheymakeupsomeoftheoldestlineagesofgreenalgaeandarethereforerepresentativeofthefirstgreenalgaetoevolve.
Chlorophytesareagroupofapproximately7,500speciesofgreenalgaethatliveinsaltwater,freshwater,andonland.Theyexhibitanumberofdifferentgrowthformsrangingfromsingle-celled species (Chlamydomonas), filamentous forms (like thegenusOedogonium),spheroidcolonies(suchasVolvox),andthedelicate,sheet-likesealettuces(Ulva).
Charophytes are predominantly freshwater or terrestrialalgae,althoughsomelive inbrackishwater(acombinationof
it's not Easy Being GreenAlgae are well known for their mutualistic relationships with fungi. Less well known, however, are their mutualistic relationships with animals. One such relationship involves the sloth, a mammal that lives in the canopy of tropi-cal forests. The sloth gets its greenish hue from the algae that live in its fur. This coloration helps camouflage the sloth, protecting it from predators. In return, the algae get a place to live and exposure to the light that is present high in the forest canopy, where sloths usually dwell.
46 Plant diversity
saltandfreshwater).Charophytes,likechlorophytes,includeadiversity of unicellular and multicellular growth forms. SomecharophytesintheorderCharales arecalledstonewortsbecauseofcalciumdepositsintheircellwalls,atraitthathashelpedpre-serveevidenceoftheminthefossilrecord.ThegenusSpirogyra contains many filamentous species commonly encountered infreshwaterlakesandponds.
RelationshipBetweenGreenalgaeandPlantsGreenalgaeshareanumberoftraitswithplants,buttheyalsodifferinimportantways.Algaelackasterilejacketlayeraroundtheirgamete-producingstructures.Inaddition,avastmajorityofalgaereleasetheirgametesintothewater,whereasthefemalegameteisretainedonthematernalindividualinplants.
Charophytesare theonlyorganismsother thanplants that producepigmentscalledflavonoids.SpeciesinthegeneraCharaandCholeochaetealsohavereproductivetraits,suchasflagellatedspermandnonmotileeggs,thataresimilartoterrestrialplants.Speciesinthesegroupsalsoretainthezygoteinthegametophytetissues,buttheylackthesterilejacketcellsfoundinplants.Sys-tematistsbelieve thatalgae in theChara lineageare the livingdescendentsofacommonancestorsharedbygreenalgaeandlandplants.Althoughsystematistsagreethatlandplantsevolvedfromagreenalgaancestor,thereiscontinuingdiscussionaboutwhetherplantsandgreenalgaeshouldbegroupedtogetherorseparately.
Red Algae (Rhodophyta) and Brown Algae (Phaeophyceae)Thedebateabouttheexactrelationshipbetweengreenalgaeandmodernplantsdoesnotextendtotheredandbrownalgae.Thesegroups differ from plants in several ways. Because they sharestructural featureswith thegreenalgae,however,andbecausethey are photosynthetic autotrophs, they are included in thisdiscussionofgroupsthatarerelatedtolandplants.
47Fungi and Algae
Brownalgaeareasmallgroupofapproximately1,500spe-ciesthatlivemostlyalongtherockyshoresofcoldoceanwaters.Kelpisanimportantbrownalgathatformsextensiveunderwater“forests.”Thekelpbodyhasthreespecializedregions:aholdfastthatanchorsthekelp,astipe(orstem),andblades(leaves).Bladesoftenhaveafloat,whichisanair-filledstructurethatholdsthekelpupright.Amongotherthings,brownalgaedifferfromplantsinthephotosyntheticpigmentstheycontain.
Redalgaearealargegroupofapproximately6,000marinespecies,mostofwhicharemulticellular.Theygettheircharac-teristiccolorfromthehighamountofreddishpigmentscalledphycobilins intheircells.Thesepigmentsareparticularlygoodatabsorbingwhatlittlelightthereisinthedeepwaterenviron-mentswheremanyredalgae species live.Thedeepestknownphotosyntheticorganismisaredalgathathasbeenfoundliv-ing268metersbelowthewater’ssurface.Often,thecellsofredalgaearecoveredbyajellylikesubstance(mucilage)orcontaindepositsofacertaintypeofmineral(calciumcarbonate);thesematerials help the red algae survive in deep water. Althoughsome red algae produce toxic substances, they do not causetheredtidesthatkillfishandothermarinelife.Redtidesareactuallycausedbypopulationexplosionsofprotistsknownasdinoflagellates.
LIchensLichensareinterestingorganismsthatdevelopfromamutualismbetweenfungiandalgaeorcyanobacteria.Morethan98%ofthefungithatformlichensareascomycetes,butafewbasidiomycetesalsoformlichens.
Inlichens,manyunicellularalgaeliveembeddedinafungus(Figure3.5).Thealgaeprovidecarbohydratesandothernutri-entstothefungus,whichinturnprovidesalivableenvironmentforthealgae.Lichensexistinextremelystressfulenvironments,suchastreebranchesorbarerock,inwhichneitherthefungus
48 Plant diversity
noralgaecouldlivealone.Thisabilitytosurviveinharshenvi-ronmentsallowslichenstobeamongthefirstcolonizersofbarerocksurfaces.
Figure 3.5 Lichens are symbiotic organisms with algae embedded in a fungal matrix. The above image is of Lobaria pulmonaria, the most widespread Lobaria lichen, photographed in Oregon.
49Fungi and Algae
Lichensdisplaythreedifferentgrowthforms.Crustoselichensareflat;theyoftenappeartobepaintedonthesurfaceswheretheygrow.Foliose lichens have a leafy appearance.Fruticose lichensrange in appearance from the multibranched individuals ofreindeermoss(Cladonia subtenuis)totheerectpillarsofBritishsoldier(Cladonia cristatella).Despitetheirabilitytotoleratethehot,dry,brightconditionsofbarerock,lichensarequitesensitivetoairpollution.Environmentalscientiststhereforeuselichensasindicatorsofairpollution.
summaRyAlthoughtheyarenotplants,fungiandalgaeareimportantinanydiscussionofplantdiversityandevolution.Fungiaremul-ticellular, heterotrophic organisms. Their ecological functionasdecomposersmakesnutrientsinthesoilavailabletoplants.Symbiotic relationships with mycorrhizal fungi allowed earlyplants to colonize the land, and continue to help them still.Greenalgaeareadiversegroupofunicellularandmulticellularphotosyntheticorganismswhosecharacteristicsindicatethatallterrestrialplantsevolvedfromasinglealgalancestor.
50
seedlessnonvascularPlantsTheBryophytes
. . . the peat of the valley of the Somme is a formation which,in all likelihood, took thousands of years for its growth.
—Charles Lyell (1797–1875)British geologist
More than 500 million years ago, a multicellular species of alga becamethefirstorganismtomakethetransitionfromlivinginthewatertolivingonland.Livinginshallowwaters,thisances-torofallplantsexperiencedalternatelywetanddryconditionswiththeriseandfallofthetides.Traitsevolvedinthisspeciesthatalloweditnotonlytotoleratethedryperiodsatlowtide,butalsotosurvivefartherfromtheedgeofthewater.Fromthesesimplebeginnings,KingdomPlantaewasborn,andthebotanicalinvasionoflandhadbegun.
Plantsadaptingtolandhadtoovercomecertainchallenges;airdoesnotprovidethestructuralsupportorthenutrientsthatwaterdoes.Inresponsetothesenewenvironmentalconditions,earlyplantsbeganproducingacuticle—athickenedlayerofwaxymaterialontheoutersurfaceofcellsthatpreventedthemfromdryingout.Theplantswereprobably thin, allowingnutrientstoenterandspreadthroughouttheplantbody(vascular tissueforspecializedtransportwouldnotevolveforanother50to100millionyears).
Althoughoftenoverlookedbecauseoftheirdiminutivesize,bryophytes(Figure4.1)arethelivingdescendentsoftheseearli-estplants.Bryophytesarenonvascularplants. Therearebetween20,000 and 25,000 species of bryophytes (Table 4.1) classifiedinto three divisions: liverworts (Hepatophyta), hornworts(Anthocerotophyta)andtruemosses(Bryophyta).Thesemod-ernbryophyteshaveretainedmanyfeaturesoftheirancestors;forexample,theyproducenovasculartissueorseeds.Becauseofthis, thestudyofbryophytescanprovideinsightintosomeofthefirststrategiesevolvedbyplantsintheiradaptationtolifeonland.
FeaTuResoFBRyoPhyTesBryophytesaretypicallysmallplants,rangingfromafewmillime-terstoseveralcentimetersinheight.Theirsizeislimitedbecausetheylackvasculartissue,whichprovidesthestructuralsupportand nutrient transport necessary for larger growth. Instead of
52
seedlessnonvascularPlantsTheBryophytes
53
Figure 4.1 Bryophytes are small, nonvascular plants. Above, green moss (a type of bryophyte) covers three oak tree trunks.
Seedless nonvascular Plants
54 Plant diversity
usingrootstotakeupwaterandanchorthemselvesinplace(asplantsdo),bryophytesusespecializedcellscalledrhizoids.Unlikerootcells,rhizoidsdonothaveanygreaterwateruptakeabilitythantherestoftheplant.Mostbryophytesusetheirentirebodiestogatherwaterandnutrientsfromtheenvironment.
Althoughsomebryophytescansurviveinverydryhabitats,avastmajorityofbryophytesliveinmoistenvironments(Figure4.2). Bryophytes are restricted to moist environments partlybecausetheylackvasculartissue,butalsobecausewaterisrequiredforspermtoswimtotheeggsduringsexualreproduction.
BRyoPhyTeLIFecycLeThelifecycleofbryophyteshasdistinctgametophyteandsporo-phytegenerations.Thefree-livinggametophyteisthedominantphase. The short-lived sporophyte is attached to and nutri-tionally dependent upon the gametophyte. The structure andappearance of gametophytes and sporophytes differ amongbryophytegroups.
Haploid spores germinate into small, threadlike, multicel-lulargametophytescalledprotonemas.Theseprotonemasmatureand produce gametophytes with antheridia (sperm-producingstructures),archegonia (egg-producingstructures),orboth.Mostbryophytes produce antheridia and archegonia on the same
Table4.1 Major Groups of Bryophytes
Group Common name Estimated species
Anthocerotophyta hornworts 100–150
Hepatophyta liverworts 6,000–9,000
Bryophyta truemosses 12,000–15,000
55Seedless nonvascular Plants
Figure 4.2 Mosses are common in moist, streamside habitats. In this photograph, moss is present on a boulder near Silverton, Colorado.
56 Plant diversity
gametophyte,butmossesproduceantheridiaandarchegoniaonseparatemaleandfemalegametophytes.
Becausethespermmustswimtotheegg,maleandfemalegametophytes must grow near one another. Sperm cells usewhiplike flagella topropel themdownanarrowcanal towardtheegg.Afterfertilization,thecombinedeggandspermformadiploidembryothatwillbecomethesporophyte.Theyoungspo-rophyteisattachedtothegametophyteandwillremainattachedtothegametophyteforitsentirelife.Asporangiumformsatthetipofthesporophyte.Sporemothercellsinsidethesporangiumwillundergomeiosistoformthehaploidsporesthatwillstartthecycleoveragain.
majoRGRouPsoFBRyoPhyTesBryophytes are a relatively small group of plants containingapproximately 24,000 species. All bryophytes are structurallysimple plants, and the major groups differ primarily in theirreproductivestructures.
Figure 4.3 Marchantia is a typical liverwort. It is a primitive plant related to mosses and ferns.
57Seedless nonvascular Plants
LiverwortsLiverwortsarethesecondlargestbryophytedivision,with6,000–9,000species.Thebasicbodyformofaliverwortconsistsofasimple,flattened,leaflikethallus,thathasaverysimplebranchingpattern(Figure4.3).Theseplantsareinacladecalledtheleafyorsimplethallusliverworts.Theremainderoftheliverwortsareinacladecalledthecomplexthallusliverworts.Theseplantshaveabroader,flattenedthalluswithpronouncedstructuraldiffer-encesbetweentheirupperandlowerlayers.
Thegenus Marchantiacontainsspeciescommontocool,shady,moistareasnearstreamsandwaterfalls.Marchantia producessep-aratemaleandfemalegametophytes.Themalesproduceanther-idiaonraisedflattenedstructureswhich,whenhitwithadropofwater,launchthespermfromthegametophye.Femalesproducearchegoniaonaraisedstructurethathasadroopingappearance.The sporophyte is a small, rounded structure attached to theundersideofthefemalegametophyte.Gemmae (singular:gemma)aresmallmassesoftissuethatmayformincuplikestructuresonthethallus.Thesemassesofvegetativecellscansplashoutofthecups, allowing theparentplant to reproduceasexually throughvegetative reproduction.Marchantiamayalsoreproducevegetativelybyfragmentationofpartsfromalarger,olderplantbody.
doctrine of SignaturesLiverworts and an assortment of other plants include the names of various organs in their common names. This comes from a belief known as the Doctrine of Signatures. Early physicians and herbalists thought a plant that resembled an organ could be used to treat ailments of that organ. The lobed liverwort thallus was used to treat liver complaints because it resembles a human liver. The suffix -wort comes from the Old English word wyrt, meaning “herb.” The Doctrine of Signatures was a popular medical concept through the nineteenth century and is still used by some practitioners of homeopathic medicine.
58 Plant diversity
HornwortsHornwortsarethesmallestbryophytedivision,with12generaandonly100–150species.Liketheliverworts,theyproduceantheridiaandarchegoniaontheuppersurfaceofathallus.Inhornworts,however, the sporophyte grows from the upper surface of thethallusandhasanelongatedhornorspindleshape(Figure4.4).Hornworts resemblevascularplants in that their sporophyte isphotosyntheticandproducesstomata(openingsthatallowwaterandgassestobeexchangedbetweentheplantandtheatmosphere).Theproductionofstomatamaybeanimportantevolutionarylinkbetweenhornwortsandplantsthatevolvedlater.
MossesThemostfamiliarofthebryophytes,mosses,areaverysuccessfulgroup,with12,000–15,000species.Theygrowinawiderangeofconditionsrangingfrommoistareasalongstreamsandinforeststoarcticandalpineenvironments.Mossesaretypicallydividedinto
Figure 4.4 Hornworts are most commonly found in damp, humid, undisturbed locations. Hornworts are seen here in Lincoln County, Oregon.
59Seedless nonvascular Plants
threeclasses:peatmosses(Sphagnopsida),granitemosses(Andre-aeopsida), and true mosses (Bryopsida). The peat mosses are asmallgroupwithtwogeneraandmorethan400species.Sphagnum peatbogs coverapproximately1%oftheEarth’ssurface.Granitemosses areaneven smallergroupof approximately100 species.These blackish-green or reddish-brown mosses grow in clumpsinmountainsandgraniteoutcrops.Thetruemossesarethemostcommon.Althoughindividualplantsaresmall,mossgametophytescandominatethelandscapewithextensivematsofvegetation.
Themosssporophytegrowsfromthetopofthefemalegame-tophyte.Thematuresporophyteiscomposedofacapsuleonthetipofalongstalkcalledaseta.Whenmature,thecapsuledries,releasingthenumeroussporesinside.
Similartovascularplants,mossesproducespecializedtrans-portcells.Cellscalledhydroidsarefoundinthecentralstemofsomemossspecies,andfunctiontotransportwaterupthemossstem.Cellscalledleptoidstransportsugars.Althoughtheyfunc-tionlikevasculartissue,hydroidsandleptoidslacksomeofthedefining features of true vascular tissue. Many mosses have aleafyappearancewithareasofphotosynthetictissuethatresem-bleleaves.Becausethesestructureslackvasculartissue,however,theyarenot true leaves.Nevertheless, suchfeatures indicateacloserelationshipbetweenmossesandvascularplants.
A Moss By Any other nameConfusion between common and scientific names is nowhere more evident than in the term moss. Technically, mosses are the plants in the group Bryophyta. The name moss, however, is applied to various plants and nonplants outside of this group. Irish moss and the moss in ponds and lakes are actually algae. Spanish moss and rose moss are angiosperms. Club moss and spike moss are seedless vascular plants related to ferns. Reindeer moss is not a plant at all, but rather a lichen.
60 Plant diversity
oRIGIns,DIVeRsIFIcaTIon,anDPhyLoGenyoFTheBRyoPhyTesSporesandfragmentsofancientbryophyteshavebeenfound infossilsthatdatebackalmost445millionyears(Table4.2).Thesefos-silsandotherdatasuggestthatbryophytesevolvedfromtheiralgalancestorbetween490and500millionyearsago.Bryophytesprob-ablydivergedfromthelineagethatgaverisetovascularplantsabout430millionyearsago.Fossilsofancientliverwortshavebeenfound
Table4.2 The Geological Timescale
Eras Periods Beginning (mya)* Major botanical events
Quarternary 1.8
Cenozoic Tertiary 65 Radiationoffloweringplants
Cretaceous 144 Evolutionoffloweringplants
Mesozoic Jurassic 206
Triassic 248 Conifersdominant
Permian 290
Carboniferous 354 Forestsoflarge,primitivetrees
Paleozoic Devonian 417 Seedlessvascularplants
dominate,firstseedplants
Silurian 443 Firstvascularplants
Ordovician 490 Plantsinvadeland
Cambrian 543
Precambrian 4550 FormationofEarth
*mya:millionyearsago
61Seedless nonvascular Plants
inrocksdatingback360to408millionyears,andmossfossilshavebeenidentifiedfromasfarbackas290to360millionyearsago.
Untilrecently,allbryophyteswerethoughttohavedescendedfromasingle,commonancestor.Newevidenceindicates,how-ever, that bryophytes are actually three distinct monophyleticlineages.Thearrangementofthethreelineages,however,isnotcompletely certain. Traditionally, systematists believed horn-wortstobeoldest,withliverwortsthenextoldest,andmossesthemost recentlyevolvedgroupofbryophytes.Somestudies,however, have suggested that hornworts may actually be themostcloselyrelatedtovascularplants.
ecoLoGIcaLanDeconomIcImPoRTanceEcologically, bryophytes are important plants. They grow inextensive mats and colonies that can help stabilize soils nearstreams.Theymaycolonizedisturbedsitesearly,beginningtheprocessofecologicalsuccession inwhichtheplantsgrowingonasitechangesovertime.Mossesareimportantcomponentsoffoodchainsinmanyarcticandalpineenvironments.
Economically, bryophytes are of some importance. Sphag-num mosshasavarietyofdifferentuses.Inthepast,it wasusedtodressandpackwounds.Peat,whichislargelySphagnum, isburnedasfuelinsomenortherntemperateareas,inhomesandinlarger-scaleelectricityproduction.Peatisalsoimportantinthehorticultureindustrywhereitisusedtolightenandincreasethewater-holdingcapacityofsoil.
summaRyLiverworts, hornworts, and mosses are nonvascular, nonseed-producingplants.Knowncollectivelyasbryophytes,thesewerethe firstplants tosuccessfully invade,establish,andpersistonland. True to their aquatic origins, however, they still dependonwatertotransportspermtoeggduringsexualreproduction.Bryophytes are the only plants with a dominant gametophytestageandasmallersporophytestage.
62
seedlessVascularPlants
Nature does not proceed by leaps and bounds. —Carolus Linnaeus
The coal that powered the Industrial Revolution in the eighteenthandnineteenthcenturiesisstillanimportantfuelsourcetoday.Coalformationbeganmorethan300millionyearsago,whenshal-lowseascoveredtheEarthandawarmtropicalclimatepromotedlushplantgrowth.Treesandplantsthatfellintothewaterastheydieddidnotdecomposebecausethelowoxygencontentofthewaterpreventedit.Overtime, layersofsedimentsaccumulatedontopoftheplants,whichforcedthewateroutoftheirtissues.Duringthecourseofmillionsofyears,theintensepressureandheatofgeologicforcesconvertedtheplantsintocoal.
Onegenusof tree, inparticular, contributedagreatdealofplantmattertothecoalbeds.ThetrunksofLepidodendron treesstoodmore than130 feet (40meters) tall andweremore than6 feet (2 meters) in diameter. They and their relatives formedextensive forests. Lepidodendron and many of the other plantsthateventuallybecamecoalweremembersofagroupcalledtheseedlessvascularplants.Unlikethebryophytesbeforethem,theseplantsevolvedvasculartissue,anetworkofxylemandphloemthattransports water, nutrients, and other materials efficiently andeffectivelyaroundtheplantbody.Thisandotherimportanttraitsmadethenextgreatbreakthroughinplantevolutionpossible.
Many different lineages of seedless vascular plants havebecome extinct since they first evolved. At present, seedlessvascularplantsconsistofapproximately14,000species intwomonophyletic clades (Table 5.1). The oldest clade, the lyco-phytes (division Lycopodiophyta), contains three orders: theclubmosses(Lycopodiales), spikemosses(Selaginellales),andquillworts (Isoetales). The second clade, previously known asthefernsandfernallies,isthemonilophytes. Thisclade containshorsetails(Equisetales),whiskferns(Psilotales),ophioglossoidferns (Ophioglossales), marattioid ferns (Marattiales), waterferns(SalvinialesandMarsileales),andthetrueferns(Filicales).Themonilophytessharedacommonancestorwiththelineagethateventuallygaverisetoseedplants.
64
seedlessVascularPlants
65Seedless Vascular Plants
FeaTuResoFseeDLessVascuLaRPLanTsSeedlessvascularplantswerethefirsttoevolvevasculartissue.These plants, along with the gymnosperms and angiosperms,formagroupcalledthetracheophytesorvascularplants.Themostprimitivetypeofwater-conductingcells,tracheids, arefoundinthexylemofseedlessvascularplants.Thesecellsarerigidduetothepresenceofligninintheircellwalls.Networksoftracheidsnotonlyaidthepassageofwater,butalsosupporttheplantbody.This internal reinforcement of the stem allowed plants of theCarboniferoustoreachgreaterheightsthaneverbefore.Eventu-
Table5.1 Major Groups of Seedless Vascular Plants
Group Common name Estimated species
Lycopodiales clubmosses 380–400
Selaginellales spikemosses 700–750
Isoetales quillworts 125
Psilotales whiskferns 15–17
Equisitales horsetails 15–25
Ohioglossales ophioglossoidferns 75–110
Marattiales marattoidferns 200–240
Marsiliales waterclover 75
Salviniales waterspangles, 16
mosquitoferns
Filicales trueferns 11,500–12,000
66 Plant diversity
ally,plantsevolvedthemechanismstoproduceandaccumulatexyleminthestem,whichledtotheevolutionofwoodandevenstrongerstemsandbranches.
Withvascular tissue,cametheevolutionof leaves.Leavesarethin,flattenedareasofphotosynthetictissuesurroundinganetworkofveins.Leavesevolvedfromhighlybranchedstemsof early vascular plants, when photosynthetic tissue filled inthespacesbetweenthefinestbranchesatthetipsofthestems.Vascularplant leavesandstemshavea thickcuticle layerontheiroutersurfacethatpreventswaterloss.Leavesalsobecamemuchmoreelaborateandstructurallydiverseinseedlessvas-cularplants.Thefernsinparticularevolvedlargeleavescalledfrondsthatproducesporangiaontheirundersideinmanyspe-cies(Figure5.1).
Plants were evolving new structures below ground as well.Instead of the simple rhizoids that attach bryophytes to theground, the first vascular plants evolved roots. Larger rootsenabledplantstoextractwaterandnutrientsfromthesoilmoreeffectively. Larger roots also provided a stronger anchor andbetterstructuralsupporttothelargerstemsthatwereevolvingaboveground.
Thelifecycleofseedlessvascularplantsalsodivergedfromthat of their bryophyte ancestors. While the sporophyte inbryophytesissmallandcompletelydependantuponthegame-tophyte, the gametophyte and the sporophyte in the seedlessvascularplantscanbeafree-livingplant.Furthermore,unlikethebrypophytes,thesporophytedominatesthelifecycleinseed-lessvascularplants.
Thesechangesinthevasculartissue,leaves,andsporophytepromotedthesuccessof theseedlessvascularplants.Vasculartissueandleaveshelpedplantssurviveinaterrestrialenviron-ment and allowed them to colonize drier areas on land. Thedominant sporophyte also allowed the plants to produce farmoreoffspringthanbryophytes.
67Seedless Vascular Plants
seeDLessVascuLaRPLanTLIFecycLeThe life cycle of a typical fern serves as a good example ofthe alternation of generations in seedless vascular plants.Spores are released from sporangia on the undersurface ofthe leaves. The spores germinate to form an independent,heart-shaped,photosyntheticgametophyte.Atmaturity, theantheridiareleasethesperm,whichswimtoandfertilizetheegghousedinthearchegonium.Afterfertilization,theembry-onic sporophyte grows from the gametophyte, which thenwithersanddieswhilethesporophytebecomestheplantweknowasafern.
Anothersignificantchangeinvolvingthesporesoccurredintheseedlessvascularplants.Inthebryophytesandearliestvas-cularplants,allsporesproducedbyaplantareidentical(homo-
spory),producinggametophyteswithantheridiaandarchegonia(mosseshaveseparatemaleandfemalegametophytes,butthey
Figure 5.1 Sporangia are found on the underside of fern fronds. Spo-rangia contain spores, and when the walls of the sporangium dry out, the spores catapult away from the plant.
68 Plant diversity
comefromidenticalspores).Somevascularplantsevolvedtheability to produce different spores (heterospory). Microspores,producedinamicrosporangium, giveriseto malegametophytes.Megaspores, produced in a megasporangium, make the femalegametophyte.Heterosporyisavaluabletraitbecauseitallowssomegametophytestobecomespecializedforspermproduc-tionandothersforeggproduction.Thiswasanimportantsteptowardtheevolutionofpollenandseedsthatwouldoccurlaterinthegymnosperms.
majoRGRouPsoFseeDLessVascuLaRPLanTsSeedless vascular plants include a diverse array of more than25,000 species. Members of the major groups display a widerangeofgrowthforms,lifecycles,andotheradaptationstotheenvironmentswheretheylive.
LycophytesLycophytesarearelativelysmallgroupofplantswith3families,10to15genera,andapproximately1,200species.Alllycophyteshave simple leaves (microphylls) that contain a single strandof vascular tissue. Lycophytes include the club mosses, spikemosses,andquillworts.
Club MossesClubmosses(Lycopodiales)areasmallgroupwith3generaandapproximately380to400species.Thesporophyteisalow-growingterrestrialplantwithsimplebranchingstems(Figure5.2). The plant spreads by a rhizome and has rudimentaryroots.Thesmall,scalelikeleavesbeararesemblancetothoseof many conifers, hence the common name “ground pine”giventosomeclubmosses.Leavesareoppositeoneanotheronthestem.
Sporesareproducedinsporangiaonspecializedleavescalledsporophylls, whichareoftenclusteredattheendsofbranches
69Seedless Vascular Plants
into a structure called a strobilus or cone. Club moss game-tophytes are either photosynthetic or obtain nutrition fromorganic material in the soil through symbiosis with mycor-rhizalfungi.
Spike MossesTheorderSelaginellaleshasonly1genus(Selaginella) and700–750species.Thesporophyteisabranchingrhizomesimilartothat of club mosses; whereas the leaves of club mosses growoppositeoneanother,spikemossesproduceleavesinfourrows:tworowsofsmallleavesabovetworowsoflargerleaves.Theseleaveshaveascalelikestructureontheirbase.
Althoughmostspikemossesliveinthetropics,someliveindryenvironments.Theseso-calledresurrectionplantsbecomedormantwhenwaterisscarce,takingonalifelessappearance,onlytospringbacktolifewhenrehydrated.
Figure 5.2 Lycopodium is a typical club moss. Above, stiff club-moss (Lycopodium annotinum) is found in the Pocono Mountains, in Pennsylvania. Note the brown strobili at the ends of the branches.
70 Plant diversity
Quillworts Isoetalesisthesmallestlycophyteorder,withonlyasinglegenus(Isoetes)and125species.Quillwortsarerelativelysmallaquaticplantsthatliveunderwaterforpartoralloftheirlife.Thespo-rophyteisaperennialcormthatcanbesomewhatwoody.Tuftsoflong,quill-likeleaves,mostofwhicharecapableofproducingsporangia,growfromthetopofthecorm.
MonilophytesMonilophytesarea largediversecladecontainingmorethan12,000 species. All monilophytes produce megaphylls, leavesthat have multiple strands of vascular tissue. There are sixmajorgroupswithinthemonilophytes:horsetails,whiskferns,ophioglossoid ferns, marattioid ferns, water ferns, and trueferns.
Whisk FernsWhiskfernsareabsentfromthefossilrecord.Psilotalesisaverysmallorder,withonly2generaand15–17species.ThegenusPsilotumgrowsintropicalandsubtropicalareas.Psilotumhasasimplebodywithsmall,scalelikeleavesandastemthatbranchesoffintotwosmallerstems.Plantshavenoroots;theyspreadbyan underground rhizome covered with rhizoids. Both sporo-
diminutive descendents of GiantsCompared to other species of seedless vascular plants, quillworts are quite small, often being mistaken for clumps of grass—something that would never have happened to their lycophyte ancestors. Recent analyses have shown that the small quillworts of today are the living descendents of the giant lycophyte trees that once dominated swamp forests more than 350 million years ago. Why only small plants from the different seedless vascular plant lineages survived to the present is a mystery that botanists are still trying to solve.
71Seedless Vascular Plants
phytesandgametophytesformrelationshipswithmycorrhiozalfungi.Psilotum hasdistinctivesporangiathatareborneinclustersofthreeonthestem.
HorsetailsEquisetaleswasonceadiversegroup,butitnowcontainsonlyasinglegenus(Equisetum)with15–25species.Thehorsetailsareperennialsthatgrowinmoistareasandalongwaterways.Although modern horsetails may reach heights of about 1meter, ancient horsetails known as calamites grew to treesize.
Horsetails have a unique appearance. Branching rhizomessend up aerial stems, whose silica deposits give them a roughtexture.Theridgedstemisessentiallyahollowtubeofseparatesegments.Atthejointsofthesegmentsthereareringsofsmall,scalyleaves.Ovalsporangiaatthetipsofthestemsproducethespores.
Ophioglossoid FernsOphioglossales, also called adder’s tongue ferns, are a smallgroupwith80–90species.Theleavesofthesefernsaredividedintotwodistinctregions:onethatisphotosyntheticandsterile,and another that is nonphotosynthetic and produces spores.YoungleavesofOphioglossoidfernsarenotcoiledasinothergroups.Theyalsoproduceuprightstems,whichdifferfromthehorizontalstemsoftrueferns.Thesporangiaofophioglossoidfernsdevelopfromagroupofcells,unlikethesporangiaoftruefernsthatdevelopfromasinglecell.
Marattoid FernsMarattialesisalsoasmallgroup,withonly6generaandabout200species.Marattoid ferns, likeOphioglossoids,produceuprightstems.Their leavesare large, andwhenyoung,arecoiled into
72 Plant diversity
astructurecalledafiddleheadorcrozier that uncoilsasitopens(Figure5.3).Thesefernsalsoproduceasporangiumthatdevel-opsfrommultiplecells.Thesefernswerecommoninswampsandarewellrepresentedinthefossilrecord.
Figure 5.3 The fiddlehead is an identifying feature of marattoid and true ferns. Above, a fiddlehead is seen unraveling.
73Seedless Vascular Plants
Water FernsWaterfernsgrowinfreshwaterpondsandlakes.Therearetwodifferentordersofwaterferns,MarsilealesandSalviniales.Bothare small groups, with approximately 75 species in Marsilealesandonly16speciesinSalviniales.Marsileaplantsgrowinshallowwaterormudandproducefrondswithlongpetiolesandleavesthatlooklikeafour-leafclover.FernsinSalvinialesproducetwotypesoffronds;oneisflattenedandfloatsonwater,andtheotherisfeatheryandhangsbelowthesurfaceofthewater.Thefloatingfrondscontaincoloniesofcyanobacteriathatfixnitrogenforthefernand,consequently,increasethenitrogeninthewaterwheretheygrow.Despitethis,waterfernscanbepestsinsomeareas.Bothgroupsofwaterfernsencasetheirsporesinahardstructurethatcanliedormantinthemudformanyyears.
True FernsFilicalesisthelargest,mostcommongroupofseedlessvascularplants.Therearemorethan11,000speciesin320generadividedamong 30–35 families. As mentioned previously, true fernshaveseveralfeaturesthatseparatethemfromotherferngroups.Theirstemstypicallygrowhorizontallyasrhizomes,andtheiryoungfrondsformfiddleheads.Truefernsarehomosporous.Theirsporangiadevelopfromsinglecellsontheundersurface
noxious Weedy FernsMany ferns are attractive and desired plants. Others, however, are not. Two water ferns, Salvinia molesta (kariba-weed) and Azolla pinnata (feathered mosquito fern) are aggressive, noxious weeds that can clog waterways and cause flooding. Bracken fern (Pteridium) can invade pastures and choke out native pasture plants. This is particularly problematic because bracken fern fronds contain chemicals that are toxic to cattle that eat them.
74 Plant diversity
of fronds. Sporangia are clustered into structures called sori
(singular:sorus)thatareoftencoveredbyaflapoftissuecalledan indusium. Each sporangium has a thickened layer of cellscalledanannulusalongonesideofthesporangium(Figure5.4).Tensiongeneratedbytheannuluscausesthematuresporan-giumtoopenandflingsporesawayfromtheparentplant.
Truefernsgrowinmanytemperateecosystems,buttheyareparticularlycommonintropicalareas.Fernsdisplayadiversityofgrowthforms,includingvines,smallherbs,andevenaquaticherbs. Large tree ferns grow in many tropical forests (Figure5.5).Smallerfernsarecommoninthemiddlelayers(knownas
Figure 5.4 The annulus is a thickened area on the fern sporangium. Above, spores are released from the sporangium.
75Seedless Vascular Plants
Figure 5.5 Tree ferns are the largest living, seedless vascular plants. The above image shows tree ferns in Malaysia.
76 Plant diversity
theunderstory) offorestsworldwide.Somefernspeciesdonotproduceasporophytestageatallandexistonlyasgametophytes.Thus,thesespeciesonlyreproduceasexually.
oRIGInsanDReLaTIonshIPsoFseeDLessVascuLaRPLanTsTheoldestvascularplantfossilsareofCooksoniaanddatebackapproximately410millionyears(Table4.2).Theseweresmall,simple,leaflessplantsthatspreadbybranchingrhizomes.Theyspreadbyacentral stemthatgrewalongthegroundandpro-duceduprightbrancheswithsporangiaattheirtips.Theylackedroots,andappeartohaveusedsymbioticrelationshipsbetweentheirrhizoidsandfungitoimprovenutrientuptakefromthesoil.Woody growth evolved approximately 380 million years ago.Productionofwoodevolvedindependentlyinseveraldifferentlineages.
The early vascular plant lineages Rhinophyta, Zosterophyl-lophyta,andTrimerophytadominatedthelandscape425to370millionyearsago,butallthreelineageswereextinctbyabout360millionyearsago.Duringthistime,manyspeciesbecameextinctduetothedryingoftheenvironmentthatoccurredduringthattime.Onlytheferns,herbaceous lycophytes,andhorsetail lin-eagessurvived.
Seedless vascular plants can be divided into two distinctmonophyletic clades (lycophytes and monilophytes) that arewellsupportedbyfossil,genetic,andstructuraldata.Thesplitbetweenthelycophytecladeandothervascularplantsprobablyoccurredmorethan400millionyearsago.Thesplitbetweenthemonilophytecladeandtheseedplantsoccurred20–30millionyearslater.
VaLueoFseeDLessVascuLaRPLanTsSeedlessvascularplantsarecomponentsofmanyterrestrialeco-systems.Livingseedlessvascularplantsareoflimitedeconomicvaluebeyondtheirusefulnessinlandscapingandashouseplants.
77Seedless Vascular Plants
Fiddleheadsfromsomespeciesareedible,andclubmosssporeswereonceusedasanexplosiveinfireworksandinthedevelop-ment of photography. Long-dead seedless vascular plants thatbecamecoal,however,areofimmensevalueasaneffectivefuelsource.
summaRySeedless vascular plants evolved more than 400 million yearsago.Theevolutionofvasculartissueenabledplantstobecomelargerbecauseofincreasedstructuralsupportandmoreefficienttransportofmaterialsaroundtheplantbody.Initiallyquitesmall,seedless vascular plants diversified and evolved many massivespecies thatwereonce thegiantsof theancientswamps.Pres-ently,therearetwomajorlineagesofseedlessvascularplants,thelycophytesandthemonilophytes.
78
nonfloweringseedPlantsTheGymnosperms
The pine tree lives a thousand years.The morning glory flower lives a single day.
Yet both fulfill their destiny. —Chinese proverb
The Namib Desert, one of the driest places on Earth, is home to oneofthestrangestplantsonEarth.Welwitschia mirabilissurvivesbyproducinglongtaprootscapableofaccessingwaterfromdeepinthesoil(Figure6.1).Theplantsalsocollectwaterfromcoolfogsthatblowinfromtheocean.Dropletsofwaterthatcondenseontheplant’sleavesflowdownthemtowaterthesoilaroundtheplant.
Unlike other members of the plant kingdom, Welwitschia producesonlytwoleavesduringitsentirelifetime,whichmaylastas longas2,000years.Theleavesemergefromthegermi-nating seed as the plant grows. Harsh desert winds shred theleaves,whichcontinuetogrowfromtheirbase.Theleavesandreproductivestructuresknownasstrobili,orcones, growfromtheedgeofthewoody,bowl-shapedstem.
Welwitschia belongs toagroupofplantscalled thegymno-sperms. The name gymnosperm comes from the Greek wordsgymnos(naked)andsperma(seed). Theseseedsareconsidered
80
nonfloweringseedPlantsTheGymnosperms
Figure 6.1 The desert plant, Welwitschia mirabilis, is photographed in the Namib Desert in Namibia. An adult Welwitschia consists of two leaves, which are torn into strips when the leaves are whipped by strong winds.
81nonflowering Seed Plants
to be naked because they are not covered by sporophyte fruittissues,asangiospermseedsare.ScottishbotanistRobertBrown(1773–1858) was the first to classify gymnosperms as a groupseparatefromtheotherseedplants,basedonthesenakedseeds.
Figure 6.2 Conifers are cone-bearing seed plants that display a vari-ety of shapes and sizes. Above, conifers surround a lake in northern Wisconsin.
82 Plant diversity
Thereareapproximately840 speciesofgymnosperms rep-resentedby4divisions,theconifers(Coniferophyta;seeFigure6.2),cycads(Cycadophyta),ginkgos(Ginkgophyta),andgneto-phytes(Gnetophyta).Somearerestrictedtowarmtropicalareaswhileothersformextensiveforestsincolder,higherlatitudesandareasofhighelevation.Somegymnospermsaregrowncommer-ciallyfordifferentuses.
FeaTuResoFGymnosPeRmsSeedsandpollenaretwofeaturesthathaveenhancedtherepro-ductivesuccessofgymnosperms,allowingthemtoevolveanddiversify. Seeds are an important evolutionary innovationbecause they protect the dormant plant embryos until envi-ronmental signals cue germination. Seeds also contain storedcarbohydrates and nutrients that will feed the seedling as itbeginstogrow.
Pollenisanothercriticaltraittoevolveinthisgroup.Gym-nospermswere the firstplants toproducepollenasaway tocarryspermtotheeggforfertilization.Unlikebryophytesandseedlessvascularplantsthatreleasetheirspermintotheenvi-ronment,thespermcellsofgymnospermsareencasedinpollengrainsthataretransported,typicallybywind,toegg-contain-ingovulesonfemalecones.Whenthepollengraingerminates,apollen tubegrowsintotheovule,andthespermisreleasedtofertilizetheegg.
Seedsandpollenareproducedincones(Figure6.3).Similarto the strobili in the seedless vascular plants, a gymnospermconeisagroupofsporophyllsattachedtoashortcentralaxis.Althoughsporophyllsinmostgymnospermsevolvedasamodi-ficationofaleaf,thefemaleconifercone(pinecone)isactuallynotamodifiedleaf,butratheramodifiedstemaxiscalledacone
scale.Gymnosperms are vascular plants that produce xylem and
phloem.Thegymnospermstemandrootshaveameristemcalled
83nonflowering Seed Plants
Figure 6.3 An assortment of female pine cones are displayed above, including a pine cone with open scales (a), a spruce pine cone (b), an eastern white pine cone (c), and a previous year seed cone beside clusters of male cones ( d ).
a b
c d
84 Plant diversity
thevascular cambium,whichproduceswood-formingxylemandbark-forming phloem. All gymnosperms are woody perennialplants.Amajorityofthemgrowastreesorshrubs,andmanyofthemachieveawe-inspiringsizeandage.Avastmajorityofgymno-spermsareevergreen,retaininglivingleavesontheplantthrough-outtheyear.Afew,however,suchaslarch(Larix)andbaldcypress(Taxodium)aredeciduous,sheddingtheirleavesonceayear.
GymnosPeRmLIFecycLeThegymnospermlifecyclediffersfromthoseofbryophytesandferns in its dramatic reduction of the gametophyte stage andincreaseinthesporophytestage.Thesporophyteisclearlythedominant phase. At no point in the gymnosperm life cycle isthereafree-living,independentgametophyte.
Thelifecycleofpines(Pinus) servesasagoodexampleofatypicalgymnospermlifecycle.Thematurepinetreeistheadultsporophyte.Femaleconesareproducedontheendsofbranches.Each female cone is composed of numerous cone scales withfemalesporangiaonthem. Ineachfemalesporangium,aspore
Gymnosperms of unusual Size and AgeSome of the oldest and largest organisms on Earth are gymnosperms. Several bristlecone pines (Pinus longaeva) in the White Mountains of eastern California are more than 4,700 years old. These plants, whose seeds germinated before the pyramids of Ancient Egypt were built, are the oldest known living organ-isms. A coast redwood (Sequoia sempervirens) in the Sierra Nevada Mountains of coastal California is the tallest tree on Earth, standing more than 365 feet (112 meters) tall and calculated to be more than 3,200 years old. The giant sequoia, (Sequoiadendron giganteum), which also grows in California, is another tall gymnosperm species. The tallest sequoias are more than 276 feet (84 meters) tall and 3,500 years old.
85nonflowering Seed Plants
mother cell undergoes meiosis to form four spores, but onlyone survives. The single surviving spore undergoes numerousdivisionsbymitosistoformamulticellularfemalegametophytesurroundedbyathinlayeroftissuecalledthe integuments. Thesmallopeningintheintegumentiscalledthemicropyle. Thefemalegametophyteandintegumentsformastructurecalledthe ovule.Insidetheovulearemultiplearchegonia,eachcontaininganegg.
Inthesmall,paperymalecones(Figure6.3d),sporemothercellsundergomitosistoformspores.Eachsporedevelopsintoapollengrainthatcontainsatube cellandagenerative cell.Pineandothergymnospermpollengrainsoftenformairsacs thathelpcarrythemonthewindtothefemalecones.Pollination occurswhenthepollengrainiseitherblowndirectlyintothemicropyleortrappedonadropletofwatersecretedfromthemicropyleanddrawnintoit.Thepollengrainmakescontactwiththefemalegametophyte,germinates,andslowlygrowsapollentubeintothe female gametophyte tissue. When the pollen tube reachesthearchegonium(aprocessthatcantakeuptoayear),itreleasesthespermcelltofertilizetheegg.Theembryoproducedinthefemale gametophyte tissue begins to form a seed. As the seeddevelops during the course of another year, the female conematures,formingthefamiliarwoodypinecone.Oncetheseedsaremature,theconescalesopentoreleasethem,andthecyclebeginsagainwhentheseedgerminatestoformanewseedling.
majoRGymnosPeRmGRouPsGymnospermsarearelativelysmallgroupwithapproximately800livingspecies(Table6.1).Althoughtherearefewspecies,theyarequitecommonandoftenmaintainverylargepopulations.
ConifersWithapproximately60generaandmorethan600species,Conif-erophyta is the largest,mostwell-knowngymnospermgroup.The largest family of conifers is the Pinaceae, which contains
86 Plant diversity
the pines (Pinus), spruces (Picea), hemlocks (Tsuga), and firs(Abies).Coniferstypicallyproduceevergreen,needlelikeleaves,butthelarches(Larix)producedeciduousleaves.Coniferleaveshavemanytraits,suchasathickcuticle,sunkenstomata,andmodificationsofthexylem,thathelpthemsurviveinverycoldandverydryenvironments.
Thereareapproximately100speciesofPinus.TheyarenativetotheNorthernHemisphere,wheretheygrowinadiverserangeofhabitatsfromhotsemidesertstocoldmountainforests.Pinesproduceleavesinbundlescalledfascicles.Thenumberofneedlesperfasciclecanbeanimportanttraitfordifferentiatingspecies.Maleandfemaleconesareproducedonthesameplant.Maleconesaresmall,papery,andproducealargeamountofpollen.Theseed-producingfemaleconesarewoodyandrangeinsizefromseveralmillimeterstoseveralcentimetersinlength.Femaleconesoftenhaveuniquefeaturesthatcanbeusedtoidentifydif-ferentspecies.
Another important conifer family is Cupressaceae. Junipers(Juniperus), cedars (Cupressus), redwoods (Sequoia), and other
Table6.1 Major Groups of Living Gymnosperms
Group Common name Estimated species
Cycadophyta cycads 130–150
Ginkgophyta ginkgos 1
Coniferophyta conifers 600–650
Gnetophyta gnetophytes 70–80
87nonflowering Seed Plants
membersofthisfamilyarehighlyvaluedfortheirwood,whichisusedextensivelyintheconstructionindustryforshinglesandsid-ing.Otherspeciesarecommonlyusedasornamentalsinlandscap-ing.Somespecies,particularlyinJuniperus, producefragrantwoodthatisusedinmakingchestsandclosets.Cupressaceaeisanoldfamilywhoselineagedatesback248to206millionyears.Sequoia-dendron giganteum (giantsequoia)andSequoia sempervirens (coastredwood)ofCaliforniaaresomeofthelargesttreesonEarth.
The conifers listed previously are predominantly found inthe Northern Hemisphere. The families Podocarpaceae andAraucariaceae,ontheotherhand,arecommonintheSouthernHemisphere.Theseedsofthesefamiliesareoftenassociatedwitha fleshy structure that attracts birds. The monkey puzzle tree(Araucaria)producessomeofthelargesttreesinsoutherntropi-calforests.TheNorfolkIslandpine(Araucaria heterophylla)isacommonornamentalspecies.
CycadsCycadophyta is a very old lineage of tropical and subtropicalplantsthatevolved290to248millionyearsago.Theywereanextremelydiversegroup,buthave sincedwindled toapproxi-mately130–150speciesin11genera.
Cycadsproducelargeleavesthatareoftenmistakenforpalms. Like all gymnosperms, cycads reproduce using cones. Unlikeconifers, however, cycads produce male and female cones ondifferentplants.Theyarepollinatedbyinsects,predominantlybeetles,whichtransferpollenfrommaletofemaleconeswhilefeedingonpollenandother coneparts.Afterpollination, thepollentubegrowsintotheovuleandreleasesflagellatedspermthatswimtotheeggforfertilization.
GinkgosGinkgophyta evolved 260 million years ago.Althoughdiverseand widespread in the fossil record, only one species, Ginkgo
88 Plant diversity
biloba (ginkgo or maidenhair tree), still survives (Figure 6.4).Comparisonsoflivingplantstofossilsshowthatthisspecieshaschangedverylittleduringthepast100millionyears.
Ginkgos are attractive trees. Their deciduous fan-shapedleavesturnabrilliantyellowinautumn.Maleandfemaleconesareborneonseparatetrees.Afterpollination,thepollengrainsform highly branched pollen tubes that grow throughout theovuletissue.Oncethepollentubecontactsthearchegonium,it
Figure 6.4 Shown above are Ginkgo biloba leaves and female cones. Ginkgo biloba is an ancient gymnosperm species, whose extract is commonly used as a memory enhancer.
89nonflowering Seed Plants
burstsandreleasestheflagellatedspermthatswimtotheeggforfertilization. The fleshy femaleginkgocones are infamous fortheirstench,resemblingacombinationofoldcheeseandfeet.Hence,mostornamentalplantingsconsistofmaletrees.
GnetophytesGnetophytesarequitedistinctinappearancefromoneanotherand other gymnosperms. Structural and genetic data stronglysupportGnetophytaasamonophyleticgroup.Thislineagecon-tainsthreegenera:Welwitschia, Gnetum,and Ephedra.
Welwitschia mirabilis,describedatthebeginningofthischap-ter,isthelonememberofthisgenus.PlantsinthegenusGnetumarewoodytropicalvineswhoseleavesresemblethebroadleavesofangiosperms.Thereareapproximately30Gnetum species.
Theremaininggenus,Ephedra(Mormontea)hasapproxi-mately 40 species, most of which grow in the arid regions ofthe western United States and Mexico (Figure 6.5). They aretypicallyshrubbyplantswithjointedphotosyntheticstemsandsmall, scalelike leaves. Ephedras produce the chemical ephed-rine,whichactsasastimulantandcanbeusedtotreatallergiesandrespiratorydisorders.
Living FossilsPaleobotanists recognized species of ginkgos and dawn redwoods from fossil records in which they were very abundant. In 1691, living ginkgo trees were “discovered” to Westerners by Engelbert Kaempfer, who found them growing in the temple grounds of Buddhist monks in China and Japan. In 1941, an unknown tree species was seen in a forest in China. In 1948, these trees were identified as dawn redwoods, previously believed to be extinct. Finally, in 1994, 39 trees of a gymnosperm species (Wollemia nobilis, Araucariaceae) thought to be extinct were found growing in a remote forest in Australia.
90 Plant diversity
Figure 6.5 Ephedra, commonly referred to as Mormon tea, are shrubby plants that grow in arid environments, such as Arches National Park in Utah (above). Mormon tea was used by Native Americans to make a stimulating drink.
91nonflowering Seed Plants
Gnetophytesareofparticularimportancetobotanistsbecausethey share interesting similarities with flowering plants. Forexample,maleconesproducepolleninstructuresthataresimi-lartoanthersfoundinflowers.Likewise,modifiedleavescalledbracts are often associated with male and female gnetophytecones,muchthesamewaythatmodifiedleavesareassociatedwithflowers.Mostimportant,however,thereproductivepro-cessofgnetophytesisverysimilartothatofangiosperms.
In all other gymnosperms, the pollen grain produces twospermcells,onlyoneofwhichfertilizestheegg.Ingnetophytes,onespermfertilizestheeggandtheotherfuseswithanon-eggcellinthefemalegametophyte.Thissecondfertilizationformsa short-lived embryo that eventually degenerates, but it mayprovide some nourishment to the other developing embryo.Thisprocessoftwofertilizationeventsissimilartotheoneinangiosperms, and may suggest a common ancestor betweengnetophytes and angiosperms. Some structural data suggest,however,thatgnetophytesaremorecloselyrelatedtopinesandarenotancestorstotheangiosperms.
oRIGInsanDReLaTIonshIPsoFGymnosPeRmsFossilevidenceindicatesthatseedplantsfirstevolvedapproxi-mately 365 to 380 million years ago. The oldest known gym-nospermfossilsareofaplant in thegenusArchaeopteris. It isamemberofagroupreferredtoastheprogymnosperms, whichmeans“beforethegymnosperms.”Archaeopteriswasatreelike,woodyplant.Ithadleavessimilartofernfrondsandproducedseedsinsporangiaattachedtothebranches.Otherprogymno-sperm fossils have features indicating that they evolved fromseedlessvascularplants.Seedplantsevolvedfromtheseprogym-nospermancestors.
Several diverse lineages of seed-producing plants evolvedduring the 65 million years that followed. One group calledseed fernshadfernlikeleavesthatproducedseedsattheirtips.
92 Plant diversity
Another important group, the cordaites (Cordaitales), con-tainedtreesandshrubs thatresembledmodernconifers.Seedfernsandcordaitesbecameextinct290to248millionyearsago,butthey,alongwithlycophytesandcalamites,weredominantplantsbeforethattime.
Cycadeoids (Bennettitales) are another extinct gymno-spermlineage.Cycadeoidsareinterestingbecausetheyaretheonly gymnosperm lineage to produce cones containing bothmale and female structures. Cycadioids, cycads, and ginkgosevolved248to206millionyearsagoanddiversified206to144millionyearsago.Cycadeoidsbecameextinctapproximately65millionyearsago,butthetwootherlineagesexiststilltoday.Although theyhave lost someof theiroriginaldiversity, thishighlysuccessfulgroupofplantshasexistedformorethan145millionyears.
Becausesomeoftheearliestgymnospermlineagesareknownonly from fossils, there is uncertainty about the relationshipsamongthem.Severaldifferentphylogenieshavebeenproposedforlivinggymnosperms,eachwithitsownstrengthsandweak-nesses, depending upon the data used to construct the phy-logeny. As described earlier, some botanists have concludedthat gnetophytes are the gymnosperm lineage that shared themostrecentcommonancestortoangiospermsbecauseoftheirsimilar fertilization process (called the anthophyte hypothesis).Although there are compelling reasons that support this con-clusion,currentstructuralandgeneticdatasuggeststhatangio-spermsdivergedfromthegymnospermslineageveryearly,andthat gymnosperms continued to diversify (called the gne-pine hypothesis).Cycadsandginkgosarecloselyrelatedbasallineagesinthegymnosperms.Thepresenceofflagellatedsperminthesetwogroupsalsoindicatesthattheseareoldergymnospermlin-eages.Nonpine conifers compriseone remaining lineage, andPinaceae conifers and gnetophytes evolved from a commonancestor.
93nonflowering Seed Plants
VaLueoFGymnosPeRmsGymnospermsareecologicallyimportantplantsthataredomi-nantspeciesinmanyecosystemsworldwide.Inadditiontopro-vidinghabitatandfoodforotherorganisms,theyalsoshapetheirenvironmentbyaffectingsoil,wateravailability,andtemperature.
Gymnospermshavesignificanteconomicvalue.Awidevari-etyofspeciesareusedinlandscaping.Otherspeciesaregrownforfuel,lumber,andpaperpulpproduction.Pinesinparticulararetappedforresins,whichcanbeconvertedintoavarietyofcommercial products including turpentine and rosins. In thepast,pineresinscallednavalstoreswereusedasawaterproof-ingagentforwoodenships.Afewgymnosperms,suchaspiñonpinesandjunipers,areevengrownforfoodandflavorings.
summaRyGymnospermsareseed-producingvascularplants.Seedsandpol-lenareproducedinconescomposedofsporophyllsorconescales.Gymnospermsarosefromseed-producingancestorsthatevolvedmore than 365 million years ago. Gymnosperm lineages, suchas the seed ferns, cordaites, andcycadeoids,were large,diversegroupsthathavesincebecomeextinct.Conifers,cycads,ginkgos,andgnetophytesarethefourlivinggymnospermlineages.
Every tree is a HypothesisA fundamental component of the scientific method is the developing and test-ing of hypotheses. In systematics, the hypothesis is the phylogeny developed by a systematist. Because it is impossible to actually observe the entire evo-lutionary history of a group of plants, systematists develop a phylogeny based on their interpretations and conclusions from the data they collected. Other systematists can then collect and analyze additional data to test the relation-ship proposed in the original phylogeny or propose new relationships.
94
FloweringPlantsTheangiosperms
The rapid development . . . of all the higher plants within recent geological times is an abominable mystery.
—Charles Darwin (1809–1882)English naturalist
The passage on the previous page is from a letter written by Charles Darwin to his colleague, the eminent botanist SirJosephHooker.The“abominablemystery”Darwinreferredtowasthesuddenanddramaticappearanceanddiversificationofangiospermsinthefossilrecord.Fossilsofothermajorgroupsofplants showapatternof lineagesappearinggraduallyanddiversifyingslowlyoverthecourseofhundredsofmillionsofyears. Angiosperms made their first appearance in the fossilrecordapproximately135millionyearsago.Angiospermsthenunderwent a rapid proliferation and diversification 70–100millionyearsago.By60millionyearsago,amajorityof themodernangiospermfamiliesthatexisttodaywerewellestab-lished.Noothergroupofplantshasshownsuchrapidevolu-tion, diversification, and dominance of the landscape in thehistoryofEarth.
The successof theangiospermswasmadepossible largelythroughtheuniquefeaturesthatresultedfromtheevolutionofflowersandfruits.Asurveyofthemorethan250,000speciesofangiospermsrevealsanastonishingarrayofflowerandfruitstructuresandmodifications.Anotherevolutionaryadvantageof angiosperms is their diversity of growth forms and veg-etativetraits.Angiospermsrangefromminuteaquaticplants,
96
FloweringPlantsTheangiosperms
Say it With Flowers“O, my love’s like a red, red rose....” The Scottish poet Robert Burns, and mil-lions of other romantics past and present, have associate red roses with true love. Throughout history, flowers and fruits have been associated with emo-tions and other things in what is called “The Language of Flowers.” Acorns are a symbol of immortality. Foxgloves represent insincerity. Yellow poppies and corn symbolize success and riches. Several nations are also associated with flowers: peonies with China, lilies with France, and thistles with Scotland.
97Flowering Plants
suchaswatermeal(Wolffia),toagiantquakingaspen(Populus tremuloides) clonethatcovers106acresandisthelargestorgan-ismonEarth.TheirabilitytoadapttotheirenvironmenthasallowedangiospermstohaveanamazingimpactontheecologyandevolutionoflifeonEarth.Angiospermsareanimportantresourcetohumans,astheyhavebothpracticaluseandculturalsignificance.
TheFLoWeRThe word angiosperm comes from the Greek words angeion(“vessel”) and sperma (“seed”), and refers to the fact that
Figure 7.1 A typical flower consists of sepals, petals, stamens, and one or more carpels.
98 Plant diversity
angiosperms produce seeds from ovules that are completelyenclosed in sporophyte tissue. This is in contrast to gymno-sperms,whichproduceseedsfromabareovule.Specifically,theangiospermvesselisthewalloftheovarythatenclosestheseed.Thepresenceofflowersthatproducetheseseed-enclosedfruitsisadefiningcharacteristicofangiosperms.
Flowers consist of four parts (sepals, petals, stamens, andcarpels)thatarearrangedintofourgroupscalledwhorls(Fig-ure7.1).All fourwhorlsattach toastructureat thebaseofthe flower called the receptacle. The outermost whorl, orcalyx, iscomposedofgreen, leaflikesepals,whichcoverandprotect the developing flower bud. The petals of the flowermake up the next whorl, which is called the corolla. Petalsmayresembleleaves,butunlikeleaves,theyareoftenbrightlycolored,attractingpollinatorsforsexualreproduction.Sepalsandpetalsthatcannotbedistinguishedfromoneanother,asis the case with tulips and cacti, are called tepals. The calyxand corolla are called the sterile whorls because they do notproducegametes.
The stamens and carpels make up the two fertile whorls,which produce the gametes required for sexual reproduction.The stamensmakeup the thirdwhorl,which isknownas theandroecium(meaning“malehouse”).Pollencontainingthemalegamete(sperm)isproducedintheantherofthestamen,whichissupportedonastalkcalledthefilament.Theinnermostwhorlof a flower is the gynoecium (meaning “female house”), whichiscomposedofthecarpels.Carpelsaremadeofastigma,style,andovary.Thecarpelisalsocalledthepistil.Agynoeciummayconsistofoneormorecarpels.Agynoeciumcomposedoftwoormorecarpelsfusedtogetherisacompound pistil.Theovaryofthegynoeciumeventuallymaturestoformafruitcontainingoneormoreseeds.
Flowersaregroupedtogetheronaplanttoformaninflores-
cence (Figure7.2).Aninflorescencecanbecomposedofasingle
99Flowering Plants
flower(solitaryinflorescence),oranynumberofdifferentmulti-floweredinflorescences.Thestalkthatsupportsaninflorescence,whether multi-flowered or solitary, is called thepeduncle. Thestalkthatsupportsanindividualflowerwithinamulti-floweredinflorescenceiscalledthepedicel.
Figure 7.2 Shown above are the basic types of inflorescences. Inflo-rescence refers to the way in which individual flowers are arranged on the stem.
100 Plant diversity
anGIosPeRmLIFecycLeThelifecycleofalilyservesasagoodexampleoftheangiospermalternationofgenerations.Itbeginswiththegerminationofaseed,whichisthesporophytegeneration.Theseedlingdevelopsintoamatureplantthatwilleventuallyformflowers.Mostflow-erscontainbothstamensandcarpels.Insomeangiosperms,sta-mensandcarpelsareproducedinseparateflowersonthesameordifferentplants.
Withintheantheronthestamen,sporemothercellsundergomeiosistoformhaploidspores.Eachsporedevelopsintoapol-lengraincontainingatubecellandagenerativecell.Whenthepollengraingerminatesonthestigma,thetubecellcontrolsthegrowth of the pollen tube. This tube grows through the styletowardtheovary,carryingwithitthegenerativecell.Thegen-erativecelldividestoformtwospermcells.Thegrowingpollentubeisthemalegametophyte.
Within the carpel, spore mother cells undergo meiosis toformfourhaploidspores.Threeofthehaploidsporesdegener-atewhileonedivides threemore times toproduce the femalegametophyte.Theangiospermfemalegametophyteiscomposedof seven cells. The large central cell contains the two haploidpolarnuclei.Threecellsaretheantipodalsandtwocellscalledthesynergids arenexttotheegg.Thesesevencellsandeightnucleimakeupthematurefemalegametophyteand,withtheintegu-mentlayersaroundit,formtheovule.Ovulesareenclosedandattachedtothesporophytetissuesoftheovary.Thus,thefemalegametophyteisphysicallyattachedto,andnutritionallydepen-dentupon,thematuresporophyte.
Akeyfeatureoftheangiospermlifecycleisthereductionofthegametophytestage,particularlythefemalegametophyte,andelaborationofthesporophyte.Thisisexactlytheoppo-site of what occurs in bryophytes, where the sporophyte isattachedto,andnutritionallydependentuponamuchlargergametophyte.
101Flowering Plants
DouBLeFeRTILIzaTIonWhenthepollentubereachestheovule,itreleasesthetwospermcells.Onespermcellfuseswiththeeggtoformthezygotethatwill eventually become the next sporophyte. The other spermcellfuseswiththetwopolarnucleitoformtheendosperm,whichprovidesfoodforthedevelopingzygote.Thisdouble fertilizationisauniquefeatureoftheangiospermlifecycle.
Following the formationof the zygote andendosperm, theovuledevelopsintotheseedthatcontainstheplantembryoandfoodreserves,whichmaybeintheformofendospermorsugarsand starches stored in modified leaves called cotyledons. Ripeovary tissues surrounding the seed form the fruit. Ultimately,theseedisdispersedfromtheplantthroughavarietyofdifferentmechanisms.Somefruitsarefleshyandcontainsugars,lipids,orothersubstancestoenticeanimalstoeatthefruitandinternallytransporttheseeduntilitpassesthroughthedigestivetract.Oth-ershavehooks,barbs,orotherdevicesthatattachtotheoutsideof animals to disperse the seed. Once dispersed, the seed willgerminateandformthenextsporophyte.
majoRanGIosPeRmGRouPsIn 1703, English botanist John Ray divided angiosperms intomonocots (plants whose seeds have one cotyledon) and dicots
Pollination by deceptionFlowers use different combinations of color, scent, and shape to attract pol-linators. Some of the most specialized flower pollinator relationships involve orchids, whose flowers mimic the color, shape, and even scent of females in the bee and wasp species that pollinate them. Male bees and wasps, lured in by the false promise of a mate, inadvertently transfer pollen from one flower to another. Some arums (plants of the family Araceae) use a similar strategy, mimicking the stench of rotting meat. Flies, seeking a place to deposit their eggs, pollinate the flowers.
102 Plant diversity
(plantswhoseseedshavetwocotyledons).Botanistshavetra-ditionally followed this classification and continued to divideangiosperms into the Magnoliopsida (dicots) and Liliopsida(monocots)basedonavarietyoftraits,suchasthearrangementofvascular bundles(Figure7.3)andfeaturesofroots,leaves,andflowers.
Recentstudies,however,haveshownthatthedicotsareanartificial grouping of several different lineages. Some plantspreviouslyclassifiedasdicotsareactuallyancientangiospermlineagesthatarenowcollectivelyreferredtoasthebasal angio-
sperms (Table 7.1). This group consists of several families,includingtheAmborellaceae,Nymphaeaceae,andIlliciaceae.The remaining angiosperms are now referred to as the core
Table7.1 Major Groups of Living Angiosperms
Group Common name Estimated species
Amborellaceae
Nymphaeaceae
Autrobaileyales basalangiosperms 170
Nymphaeaceae,
Illiciaceae
Magnoliopsida* magnoliids 9,000
Liliopsida monocots 70,000–72,000
Magnoliopsida* eudicots 175,000–180,000
*Magnoliopsidaisthetraditionalnamegiventodicots.Atpresent
thereisnoICBNnamefortheseparatemagnoliidoreudicotclades.
103Flowering Plants
angiosperms. Thisgroupincludesthreemonophyleticlineages:magnoliids, eudicots, and monocots. The magnoliid cladecontains several ancient angiosperm families, including the
Figure 7.3 Cross-sections of monocot and dicot stems reveal the differ-ences in vascular bundle arrangement. Vascular bundles are arranged in a ring in dicots (a), but scattered in the monocot stem (b).
a
b
104 Plant diversity
magnolias (Magnoliaceae), laurels (Lauraceae), spicebushes(Calycanthaceae), and black peppers (Piperaceae). Eudicots
(true dicots) make up a large, natural group that containsabout 75% of all dicot species. Eudicots share a commonfeaturethatisnotfoundinanyotherfloweringplants:Theyhavethreeopeningsintheirpollengrainwalls.Allotherplants(gymnosperms, basal angiosperms, magnoliids, and mono-cots)producepollengrainsthathaveonlyoneopeningintheirwalls.Beyond thisdifference,magnoliidsandeudicots sharemanyotherfeatures(Table7.2).
Despitechangesinourunderstandingofdicots,monocotsarestillrecognizedasasinglelineagethatdescendedfromacom-monancestor.Monocotsaccountforapproximately22%ofallangiosperms.
Table7.2 Differences Between the Three Core Angiosperm Groups
Trait Monocots Magnoliids Eudicots
Cotyledons 1 2 2
Vascularbundle scattered ring ring
arrangementinstem
Leafveinpattern parallel pinnate palmate,
pinnate
Numberofflower three-merous many four-merous,
parts five-merous
Openingsin 1 1 3
pollengrains
105Flowering Plants
Significantdifferencesexistbetweenthefloralstructuresofeudicotsandmonocots.Ineudicotflowers,thepartsofthedif-ferentfloralwhorlsaretypicallyinmultiplesoffour(four-merous)orfive(five-merous).Forexample,membersofthemustardfam-ily(Brassicaceae)produceflowerswithfoursepals,fourpetals,and four stamens.Species in the rose family (Rosaceae), suchas roses, strawberries,andblackberries,have flowerswith fivesepalsandfivepetals.Monocotflowers,suchasirises,lilies,andtulips,arethree-merous,withthreesepals,threepetals,threeorsixstamens,andapistilwiththreecarpels.
ecoLoGIcaLanDeconomIcVaLueAngiospermsaredominantcomponentsofterrestrialenviron-mentsworldwideand,consequently,playamajorroleintheeco-logicaldynamics thatmaintainahealthyplanet.Angiospermsalsoincludemanyimportantresourcesthathumansdependonforavarietyofpurposes.Angiospermsprovidefood,ornamen-tals,fibers,andawidearrayofchemicals.
Oaks(Fagaceae),hickories(Juglandaceae),andmaples(Sap-indaceae)aremajorcomponentsof forests inmanytemperateareas. Tropical forests, however, are often dominated by treesfrom a multitude of different families, including dipterocarps(Dipterocarpaceae), laurels (Lauraceae), and figs (Moraceae).Trees in these families support numerous other life forms inforestecosystemsbyprovidingfoodandhabitats.Manyofthesefamiliesalsoprovidetimberandotherresourcesforhumans.
Therosefamily(Rosaceae)iswellknownforitsornamentalspecies, like roses (Rosa sp.) and cinquefoil (Potentilla), andalsoforitsediblespecies(Figure7.4),likeapples(Malus),andpears(Pyrus),andpeaches,plums,andcherries(allinthegenusPrunus).
Thebeanfamily(Fabaceae)isoneofthelargestangiospermfamilies. Members of Fabaceae are also called legumes, whichreferstotheuniquefruitproducedbyspeciesinthisfamily.The
106 Plant diversity
symbioticrelationshipsbetweenlegumesandnitrogen-fixingsoilbacteriagivelegumeseeds(beansandpeas)ahighproteincon-tent,makingthisanagriculturallyimportantfamily.Speciessuchasbeans(Phaseolus vulgaris),soybeans(Glycine max),fieldpeas(Vicia faba),andlentils(Lens culinaris)contributetothedietsofhumansandwildlifeworldwide.
a b
c d
Figure 7.4 The rose family includes many edible fruits. Pictured above are two ripened apples (a), peaches ready to be picked (b), ripe cherries (c), and fresh pears (d).
107Flowering Plants
Themint family(Lamiaceae) includesmanyculinaryherbsandplantsrenownedfortheirperfumes.Theflavorsandscentsof plants in the mint family come from glands on the leaves,whichproducearomaticoils.Basil(Ocimum basilicum), laven-der(Lavandula), mint(Mentha), oregano(Origanum vulgare), patchouli(Pogostemon cablin),sage(Salvia officinalis),rosemary(Rosmarinus officinalis),andthyme(Thymus)arevaluedherbsinLamiaceae.Catnip(Nepeta),coleus(Plectranthus),andbeebalm(Monarda)arepopularornamentals.
Thenightshadefamily(Solanaceae)containsmanypoisonousplants. The poisons are often powerfulalkaloids, which have arangeofeffects. Tobacco (Nicotiana),belladonna(Atropa),andjimsonweed(Datura)producealkaloidswithnarcoticeffects.Hotpeppers(Capsicum)get theirheat fromthealkaloidcapsaicin.Importantedibleplants, including tomato(Solanum lycopersi-cum)andpotato(Solanum tuberosum),arealsointhisfamily.
Thesunflowerfamily(Asteraceae)isthelargestofalleudicotfamilies,withmorethan25,000species.Itcontainsmanycom-merciallyimportantspecies,suchastheannualsunflower(Heli-anthus annuus),whichisgrownforitsseeds,oil,andflowers.Thisfamilyalsocontainscommerciallygrownornamentals, includ-ing dahlias (Dahlia), mums (Chrysanthemum), and marigolds(Tagetes),aswellasaggressive,noxiousweeds,suchasdandelion(Taraxacum officiale)andCanadathistle(Cirsium arvense).
Thegrasses(Poaceae)accountforapproximately17%ofallangiosperms. This monocot family serves as the foundation offoodwebsandotherprocessesinprairies,savannas,andtundraecosystems. Grasses can be found in most other ecosystems aswell.Nineofthetop20cropspeciesaregrasses,withcorn(Zea mays),wheat(Triticum aestivum),andrice(Oryza sativa)provid-ing50%ofhumancaloricintake.Bamboos(Bambusa)aregrassesthathaveawiderangeofuses, includingconstruction,textiles,and papermaking. Other species, such as cheat grass (Bromus tectorum) and Johnson grass (Sorghum halapense), are invasivespeciesthathaveadetrimentaleffectonnativevegetation.
108 Plant diversity
Theirises(Iridaceae),orchids(Orchidaceae),andlilies(Lili-aceae) are often called the “showy monocots” because of thebright,colorfulpetalsintheirflowers(Figure7.5).TheIridaceaeincludesirises(Iris),gladiolus(Gladiolus),crocus(Crocus), andblue-eyedgrass(Sisyrynchium).TheanthersfromCrocus sativus
a
b c
Figure 7.5 The lilies, irises, and orchids produce bright, showy flowers. Photographed above are the white lily (a), purple iris (b), and the harle-quin “dancing lady” orchid (c), also known as a butterfly plant.
109Flowering Plants
arethesourceofthespicesaffron.Orchidsarethelargestangio-spermfamily,withmorethan30,000species.Thereareterrestrialorchidsaswellasmanyepiphytes, plantsthatgrowonthestemsandbranchesoftrees.Orchidsareparticularlydiverseinthetrop-ics,wheretheyformcloserelationshipswiththeorganismsthatpollinatetheirflowers.Liliaceaecontainsornamentalsincludinglilies(Lilium)andtulips(Tulipa).Thereareseveralediblelilies,includingonion(Allium cepa),garlic (Allium longicuspis),andchives(Allium schoenoprasum).
oRIGInsanDReLaTIonshIPsoFanGIosPeRmsThe oldest angiosperm fossils are flowers and pollen that are130–140millionyearsold.TheoldestcompletefossilplantisinthegenusArchaefructus thatlivedmorethan125millionyearsago. Itwasasimpleplantwhoseflowershadnosepalsorpetals,butnumerousstamens.
One of the first hypotheses about the origins of floweringplantswasdevelopedbyEnglerandPrantl,whosuggestedthatAmentiferae,agroupintheirclassification,wasthemostprimi-tiveangiospermgroup.This conclusionwasbasedon the factthatmanyofthesetreesarewindpollinated,justlikethemoreprimitivegymnosperms.Otherresearchersconcludedthatfami-liessuchasMagnoliaceae(magnoliafamily)andRanunculaceae(buttercupfamily)werethemostprimitivebecausetheirflow-ers contain many parts. Recent genetic analyses have shown,however,thatneitherofthesefamiliesarerepresentativeoftheoldesttypeofangiosperm.Magnoliaceaeisanancientfamily,butitisnottheoldest,andRanunculaceaehasbeenshowntobeamemberoftheeudicots.
Currently,manybotanistsagree that the familiesAmborel-laceae, Nymphaeaceae, Trimeniaceae, and the order Illicialesaretheoldest living lineagesof floweringplants.Thesegroupsproduce small, simple flowers that have few parts and simplepollinationmechanisms.Collectively,theseancientgroupsform
110 Plant diversity
thebasalangiosperms.Fossilevidencealsoindicatesthatthefirstangiospermshadsmall,nondescriptflowerswithfewfloralparts.ThespeciesAmborella trichopoda(Amborellaceae)isashrubbyplant thatgrows inthe cloudforestsofNewCaledonia.Manystudieshave indicated that it is likely the living descendentoftheoldestangiospermlineageonEarth.Fossilandgeneticdataindicate that monocots, magnoliids, and eudicots diverged asseparatelineagesapproximately100millionyearsago.
anGIosPeRmsuccessAngiospermshaveevolvedanddominatedtheterrestrialenvi-ronmentlikenoothergroupofplants.Theflowerundoubtedlyisaprimaryreasonforthissuccess.Flowersenabledplantstousedifferentshapes,colors,andscentstoattractpollinators.Flowersalsofrequentlyprovideafoodrewardofpollenornectartopolli-natorsinreturnfortheserviceofvisitingflowersandtransferringpollen.Theevolutionanddiversificationoftheseinsectandbirdpollinatorsislinkedtothatoftheangiosperms.
Likeflowers,fruitsprovideafoodrewardtoanimalsthateata fruit and disperse the enclosed seeds. Fruit size, shape, andcolorhaveevolvedinresponsetonaturalselectionmediatedby
Big FlowersThe brownish-orange flowers of the giant rafflesia (Rafflesia arnoldi ) are the largest single flowers of any angiosperm. A typical Rafflesia flower can be up to 3 feet (1 m) across and weigh as much as 25 pounds (11 kg). The titan arum (Amorphophallus titanium) produces the largest inflorescence. Its flowers are very small, but they combine to form a special type of inflo-rescence called a spadix. Separate male and female flowers are attached to a central column that can be 3 to 6 feet (1 to 2 m) tall. A huge modified leaf surrounding the column gives the spadix the appearance of being a single large flower.
111Flowering Plants
theanimalsthateatanddispersetheseeds.Angiospermshaveevolvedanarrayofmechanismstodispersetheiroffspring.
Changes in the life cycle have also promoted angiospermevolution.Whiletheotherseedplants,gymnosperms,cantakeaslongastwoyearstoprogressfrompollinationtothereleaseofthematureseed,angiospermshaveacceleratedtheprocess.Pollina-tion,fertilization,andmaturationoftheseedcanoccurwithinamatterofdaysormonths.Thisaccelerationmaybeduetothenutritionalbenefitsoftheendospermforthedevelopingembryo.Angiospermsarealso theonlyseedplants tohaveevolvedtheannuallifecycleinwhichaplantcompletesitslifeinonegrow-ing season. By shortening different aspects of their life cycle,angiospermscanreproducemorequickly,therebyspeedingtheirresponsetonaturalselectionandacceleratingtheevolutionandspreadofadaptivetraits.
summaRyAngiospermsarevascularplantsthatproduceseedsfromflow-ersandenclose theseeds ina fruit.Angiospermsare themostrecently evolved group of plants, and they dominate the ter-restrial environment. The flower and fruit are key traits thatallowedangiospermstointeractwithanimalpollinatorsandseeddispersersand,consequently,undergoextensivediversification.Therearethreemajorgroupsofangiosperms:basalangiosperms,monocots,andeudicots.Manyspeciesinthesegroupsareeco-logicallyandeconomicallyimportant.
112
Algae AgeneraltermforphotosyntheticmembersofthekingdomProtista.
Alkaloid Atypeofchemicalproducedbycertainplantsthatismadeoutofnitrogenandcanbetoxicwheningested.
Alternation of generations Alifecyclethatalternatesbetweenamulticel-lularhaploidgenerationandamulticellulardiploidgeneration.
Anatomy Thestudyofanorganism’sstructure.
Androecium Themalepartsofaflower.
Angiosperms Plantsthatproduceflowersandwhoseseedsarecontainedwithinafruit.
Animalia Theanimalkingdom.
Annulus Athickenedbandofcellsonafernsporangium,whichisinvolvedinthedispersalofspores.
Anther Floralstructureinwhichpollenisproduced.
Antheridia Malereproductivestructuresthatproduceandprotectsperm.
Antipodals Thethreecellsofthefemalegametophytethatareclusteredattheendoppositetheegg.
ArbusculesSpecializedstructuresformedbymycorrhizalfungiinsideaplantcellthatenabletheplantandfungustoexchangenutrients
Archaea Thekingdomofprokaryoticunicellularorganismscontainingblue-greenalgae,methane-producingbacteria,andotherprimitivelifeforms.
Archegonia Thefemalereproductivestructuresthatproduceandprotecttheegg.
Artificial classification system Asystemofgroupingorganismsthatisbasedonarbitraryfeaturesrathertrueevolutionaryrelationships.
Asexual reproduction Formationofoffspringthatdoesnotinvolvethejoiningofeggandsperm.
Ascus (plural: asci) Asaclikecellinwhichascomycetesformspores.
Ascocarp Thefruitingbodyofanascomycete.
Autotrophs Organismscapableofsynthesizingitsownenergy.
Bacteria Agroupofunicellular,prokaryoticorganisms.
Basal angiosperms Anamegiventothemostprimitiveangiospermlineages.
113
Basidium (plural: basidia) Theclub-shapedstructureinwhichbasiomyce-tesformspores.
Basidiocarp Thefruitingbodyofabasidiomycete.
Binomial nomenclature ThesystemdevelopedbyLinnaeusinwhicheachspeciesisgivenanameconsistingoftwowords:thegenusnameandthespeciesname.
Biodiversity ThediversityoflifeonEarth.
Blades Theflattenedphotosyntheticregionsofaleaforalgae.
Bracts Modifiedleaflikestructuresthatcanbepartofaflowerorfruit.
Brown algae Groupofmulticellularalgaeusuallyfoundinmarineenvironments.
Bryophytes Non-floweringplantsthatincludemosses,liverworts,horn-worts,andquillworts.
Bud Smallembryonicfloralorvegetativeshoots.
calamites Ancientgroupofhorsetails.
calyx Theoutermostfloralwhorlconsistingofallofaflower’ssepals.
capsule Aspore-containingstructureofthemosssporophyte.
carotenoids Aclassofyellowandorangepigments.
carpels Theovule-encasingstructuresthatmakeupthegynoecium.
cellulose Themaincomponentofcellwallsinplants.
central cell Thecellintheangiospermfemalegametophytethatcontainstwohaploidnuclei;itbecomesendospermafterfusionwithsecondspermnucleus.
chitin Asubstancethatformsthecellwallsofcertainfungi.
chlorophyll Agreenpigmentresponsibleforcapturingthelightusedinphotosynthesis.Therearetwotypesofchlorophyll,aandb, whichhaveslightdifferencesinthewavelengthsoflighttheyabsorb.
chloroplasts Structureswithinplantcellsthatcontaintheenzymesandpigmentsnecessaryforphotosynthesis.
chromosomes TheorganizedstructuresofDNAinacell.
clade Agroupconsistingofanancestorandallofitsdescendants.
114
cladistics Thesystemofgroupingorganismsbasedonananalysisoftheirprimitiveandadvancedtraits.
classification Theprocessoforganizinggroupsintoahierarchicalsystem.
common name Theunofficialnamegiventoaplantbythosewholivenearit.
compound pistil Agynoeciumcomposedoftwoormorecarpelsfusedtogether.
cone Areproductivestructurethatproduceseitherpollenorseeds,typ-icallyfoundingymnospermsandothergroupsofnonfloweringplants.
cone scale Anindividualunitofthegymnospermstrobilus.
core angiosperms Groupingsthatincludethreemonophyleticlin-eages:magnoliids,eudicots,andmonocots.
corm Adryundergroundstructurefoundinperennialplantssuchasgladiolus.
corolla The(usually)conspicuously-coloredflowerwhorlconsistingofalloftheflower’spetals.
cotyledon Aleafthatprovidesnourishmenttotheplantembryodur-inggermination.
crozier Thecoiledleafofafern.
crustose Alichengrowthformthatresemblesacrustonthesubstrateuponwhichitgrows.
cuticle Awaxy,protectivelayerontheoutersurfacesofleaves.
deciduous Aplantthatlosesitsleavesduringautumnorthedryseason.
dendrograms Treelikediagramsthatillustraterelationships.
dichotomous key Alist ofpaired,contrastingstatementsusedtoiden-tifyanunknownorganismbytheprocessofelimination.
dicots Ageneraltermgiventoangiospermswhoseseedsproducetwocotyledons,nowdividedintotwogroups,thebasalangiospermsandtheeudicots.
dikaryotic Cellsinfungithathavetwohaploidnuclei.
diploid Havingtwofullsetsofchromosomesineachcell,characteristicofthesporophytegeneration.
115
diversity Ameasureofthenumberandrelativeproportionofdifferentspeciesinacommunity.
domain Thetaxonomiclevelabovekingdom.
double fertilization Atwo-fertilizationevent,characteristicofangio-sperms,whereinonespermfuseswiththeeggtoformthezygoteandasecondspermfuseswiththepolarnucleitoformtheendosperm.
Endosperm Thetissuesformedduringadoublefertilizationeventthatnourishthegrowingangiospermembryo.
Epiphytes Nonparasiticplantsthatgrowontrees.
Ethnobotanists Scientistswhostudythewaysinwhichindigenouspeoplesuseplants,particularlyformedicinalpurposes.
Eudicots Thelargestgroupofangiosperms;theyhavetwocotyledonsandthreeopeningsintheirpollengrains.
Eukaryotic Organismswhosecellscontainnucleiandmembrane-boundorganelles.
Evergreen Atreewhoseleavescanbeshedatanytimeofyear,butneverallatonce.
Evolution Achangeingenetically-basedcharacteristicsofaspeciesthroughouttime.
Fascicles Bundlesofpineneedles.
Fertile whorls Thewhorlsofaflowerthatproducegametes.
Fertilization Thejoiningofeggandsperminsexualreproduction.
Fiddlehead SeeCrozier.
Field guide Abookthatcontainssimpledescriptionsandillustrationsofplantsinanarea.
Filament Thestalkofastamen.
Five-merous Aflowerthatcontainspartsinmultiplesoffive.
Flagella Tail-likestructuresthatpropelmanyeukaryoticcells,includingsperm.
Flavonoids Aclassofpigmentsfoundonlyinplantsandafewalgae.
Float Theinflatedpartofakelpbody.
116
Flora Aguidewithdescriptions,illustrations,distributionsmaps,andkeysthatallowtheusertoidentifyplantsofaparticulargeographicalarea.
Flowers Thereproductivestructuresofangiospermscomposedofsepals,petals,stamens,andcarpels.
Foliose Alichengrowththatresemblesleaves.
Food webs Aninterlockingsystemofproducersandconsumersinanecosystem.
Four-merous Aflowerthatcontainspartsinmultiplesoffour.
Fronds Fernleaves.
Fruit Thematureseed-containingovary(orgroupofovaries)ofangiosperms.
Fruticose Alichengrowthformthatishighlybranchedanderect.
Fungi Thekingdomoforganismsthathavecellwallsandobtaintheirfoodthroughabsorption.
Gamete Ahaploidreproductivecell,eitherspermoregg.
Gametophyte Thehaploid,gamete-producingstageinthealternationofgenerations.
Gemmae (singular: gemma)Smallmassesofvegetativetissuethatformontheuppersurfaceofathallusthatcanbedispersedforasexual,vegeta-tivereproduction.
Generative cell Thecellinapollengrainthatdividestobecometwospermcells.
Genus Thetaxonomicrankbelowfamilyandabovespecies.
Germination Theresumptionofgrowthbyadormantspore,seed,orpol-lengrain.
Gills Theplatesontheundersideofthecapsofbasidiomycetefungi.
Green algae Thegroupofalgaethatgaverisetoplants.
Gymnosperms Plantsthatreproduceusingconesandbearexposed“naked”seeds(thatis,notcontainedinfruits).
Gynoecium Thecollectivetermforallofthecarpelsinaflower.
Haploid Havingonlyonesetofchromosomes.
117
Herb Anonwoodyplant.
Herbarium Aplacewherepreservedplantmaterialsarestoredforstudy.
Herbarium sheets Piecesofpaperuponwhichpressed,driedplantspeci-mensaremounted;theytypicallyprovideinformationsuchastheplant’sscientificnameandwhereandbywhomitwascollected.
HeterosporyTheproductionoftwotypesofspores:microsporesthatgiverisetomalegametophytesandmegasporesthatgiverisetofemalegametophytes.
Heterotrophs Organismsthatmustobtainenergybyconsumingotheranimals.
Holdfast Partofthealgalbodythatattachesthealgatothesubstrate.
Homospory Theproductionofonetypeofspore.
Hydroids Primitivewater-conductingcellsinmosses.
Hyphae (singular: hypha) Fungalfilaments.
indusium Aprotectiveflapthatcoversimmaturesoriinferns.
inflorescence Aclusterofflowersclosetooneanotheronastem.
integuments Protectiveouterlayersthatsurroundthesporangiumofanovule.
international Botanical congress Thegoverningbodythatestablishesrulesonbotanicalnomenclature.
international code of Botanical nomenclature (icBn) Theinternation-allyagreeduponsetofrulesthatgovernthenamingofplants.
Kingdom Thetaxonomiclevelbelowdomain.
LeavesTheflattenedphotosyntheticpartsofavascularplant.
Legumes Fruitsthatarecharacteristicofthebeanfamily.
Leptoids Primitivefood-conductingcellsofmosses.
Lichen Organismthatresultsfromasymbioticrelationshipbetweenafun-gusandanalga.
Lignin Acomponentofthehardenedcellwallinxylem,theprimarycom-ponentofwood.
Mating types Geneticallydifferentformsofalgaecapableofsexuallyreproducingwithoneanother.
118
Megaphylls Largeleaveswithmanyveins.
Megasporangium Astructureinwhichsporesareformedthatwillbecomeafemalegametophyte.
Megaspores Sporesthatgiverisetothefemalegametophyte.
Meiosis Theprocesswherebyadiploidcelldividestwicetoproducefourhaploidcells.
Microphylls Generallysmallleaveswithasinglevein.
Micropyle Asmallopeningintheseedplantovulethatthepollentubeentersforfertilization.
Microsporangium Astructureinwhichsporesthatwillbecomethemalegametophyteareformed.
Microspores Sporesthatwillgiverisetothemalegametophyte.
Mitosis Theprocesswherebyonediploidcelldividesoncetoproducetwoidenticaldiploidcells.
Monocots Angiospermswhoseseedscontainasinglecotyledon.
Monophyletic group Agroupcomposedofanancestorandallofitsdescendants.
Morphology Thestudyofthestructureandformoforganisms.
Mutualism Arelationshipthatbenefitsbothparticipatingspecies.
Mycelium Amassoffungalhyphae.
Mycology Thestudyoffungi.
Mycorrhizae Fungithatengageinsymbioticrelationshipswithplantroots.
natural classification system Asystemofgroupingorganismsthatisbasedontheirevolutionaryrelationships.
natural selection Aprocessofevolutionarychangethatoccurswhengeneticchangeproducesindividualswithgreaterreproductivesuccessorgreatersurvival.
nitrogen fixing Processofconvertingnitrogenfromagasintoabiologi-callyusefulform.
nucleus PartofaeukaryoticcellthatcontainsDNA.
119
organelles Small,specializedstructureswithinaeukaryoticcell.
ovary Theenlarged,seed-producingportionofaflowerthat,afterfertil-ization,becomesafruit.
ovules Structuresinseedplantsthatcontainthefemalegametophyte.
Pedicel Thestalkofasingleflowerinaninflorescence.
Peduncle Thestalkofasolitaryflowerorinflorescence.
Perennials Plantsthatliveformorethantwoyearsandtypicallyreproducerepeatedlythroughouttheirlives.
Petals Thepartsofaflowerthatareoftenbrightlycolored.
PetioleThestalkofaleafthatattachesthebladetothestem.
Phloem Tissuethattransportssugarsandotherproductsofphotosynthe-sisthroughoutthevascularplantbody
PhotoautotrophsOrganismscapableofformingtheirownenergyresourcesthroughphotosynthesis.
Photosynthesis Theprocessthroughwhichplantsconverttheenergyinlightintosugarsandoxygen.
Phycobilins Agroupofreddishpigmentsfoundinredalgaeandblue-greenalgae.
Phycology Thestudyofalgae.
Phylocode Anomenclaturesystemthathasnohierarchicalrankingsandrecognizesonlyclades.
Phylogeny Theevolutionaryhistoryofanorganismorgroupoforganisms.
Pistil Thecollectivetermforthefemalepartsofaflower.
Plantae Theplantkingdom.
Polar nuclei Thetwonucleilocatedinthefemalegametophyteofangio-sperms,whichfusewithaspermtoformtheendosperm.
Pollen Astructurecontainingthespermcellsinangiospermsandgymno-sperms.
Pollen tube Atubethatdevelopsfromapollengrainandcarriesthespermtotheegg.
120
Pollination Inangiosperms,thetransferofpollenfromananthertoastigma;ingymnosperms,thetransferofpollenfromamaleconetoafemalecone.
PollinatorsOrganismsthattransferpollenfromoneflowertoanother.
Polynomial Anoutdatedsystemofassigninganameofmultiplepartstoonespecies.
Progymnosperms Agroupofnow-extinctplantsthatgaverisetogymnosperms.
Prokaryotic Organismswhosecellslacknucleiandmembrane-boundorganelles.
Protista Theprotistkingdom.
Protonemas Thethreadlikegametophytesofsomenonvascularandseed-lessvascularplants.
receptacleThestructureinaflowerwherethefloralwhorlsattach.
red algae Alargegroupofmostlymulticellularmarinespeciesthatgettheircharacteristiccolorfromreddishpigmentsintheircells.
rhizoidsPrimitivestructuresthatnonvascularplantsusetoattachtotheirsubstrate.
Scientific name Theofficialnameforaplant,consistingoftwowords:thegenusandthespecies.
Seed ferns Extinctgroupoffernlikegymnospermsthatproducedseedsatthetipsoftheirleaves.
Seedless vascular plants Agroupofplantsthatincludesferns,horsetails,andclubmossesthathavevasculartissue,butreproducebyspores.
Seeds Fertilizedplantovulesconsistingofanembryoanditsfoodsource.
Sepals Leaflikeoutermoststructuresofaflower.
Seta Stalkthatsupportsthecapsuleinthemosssporophyte.
Sexual reproduction Theformationofoffspringbycombiningeggandsperm.
Shrub Awoodyplantthatproducesseveralstemsandisshorterthatatree.
Sori Theclustersofsporangiaontheleafsurfaceofafern.
121
Spadix Aspecialtypeofinflorescencefoundinsomeangiosperms.
Species Aparticulartypeoforganismthatcanbedifferentiatedfromothertypesoforganisms;allmembersofaspecieshavetheabilitytointer-breedandshareacommonevolutionaryhistory.
Sporangium Aspore-producingstructure.
Spores Single-celledreproductivestructuresinbryophytesandseedlessvascularplantsthatarecapableofdevelopingintoaplant.
Spore mother cells Cellsinaplant’sreproductivetissuethatundergomeiosistoformhaploidspores.
Sporophylls Modifiedleavesthatbearsporangia.
Sporophyte Thediploid,spore-producingstageinthealternationofgenerations.
Stamens Themalepartsofflowers,composedofantherandfilament,thatproducepollen.
Sterile jacket Alayerofcellsthatsurroundsthegamete-producingarche-goniumandantheridium.
Sterile whorls Thepartsofaflower(sepalsandpetals)thatdonotpro-ducegametes.
Stigma Thereceptivepotionofthecarpeluponwhichpollengrainsgerminate.
Stipe Thestemofabrownalgaebody.
Stomata Openingsintheleafsurfacethatallowaplanttotakeinandreleasegasses.
Strobilus (plural: strobili) Acone-likeclusterofspore-bearingleaves.
Style Thecarpeltissuethatconnectsthestigmatotheovary;pollentubesgrowthroughthestyletoreachtheovary.
Succession Aseriesofpredictable,cumulativechangesinthecompositionandcharacteristicsofaplantcommunityfollowingdisturbance.
Symbiotic Arelationshipinwhichbothindividualsbenefitfromtheinter-actionandareharmedwhentheyarenottogether.
Synergids Twocellslocatedneartheegginthefemalegametophyteofangiosperms.
122
Systematics Thestudyofevolutionaryrelationshipsanddiversity.
taxon Agroupoforganismsatanyhierarchicallevel,suchaskingdomorspecies.
taxonomy Thescienceofclassifyingorganisms.
tepal Sepalsandpetalsthatcannotbedistinguishedfromoneanother.
thallus Asimplevegetativebody,undifferentiatedintoroot,stem,orleaf.
three-merous Havingthreesepals,threepetals,threeorsixstamens,andapistilwiththreecarpels.
tracheids Elongated,thick-walledxylemcellsfoundinmostvascularplantsthatconductandsupport.
tracheophytes Anothernameforvascularplants.
tree Awoodyplantwithasingletrunk.
tube cell Thecellthatdevelopsintothepollentubeinthemalegameto-phytesofseedplants.
Vascular bundles Strandsoftissuethatcontainxylemandphloem.
Vascular cambium Alocalizedareaofcelldivisionandgrowthinplantsthatproducesnewvasculartissueandcontributestoincreaseddiameterofwoodystems.
Vascular tissue Tissueusedtotransportwaterandmineralsthroughouttheplantbody.
Vegetative reproductionAsexualreproductionthroughthebreakingoffofapartoftheplantbodytoproduceanewplant.
Whorl Anarrangementofthreeormorefloralpartsorleavesinacircle.
Xylem Tissuethattransportswaterandmineralsthroughoutthevascularplantbody
Zygospore Adormantsporeformedinzygomycetesandsomealgae.
Zygote Thediploidfirstcellofasporophytethatresultsfromthejoiningofspermandeggatfertilization.
123
Attenborough,D.The Private Life of Plants. Princeton,N.J.:PrincetonUniversityPress,1995.
BotanyOnline,TheInternetHypertextbook.Availableonlineathttp://www.biologie.uni-hamburg.de/b-online/e00/contents.htm.
Burleigh,J.G.,andS.Mathews.“PhylogeneticSignalinNucleotideDataFromSeedPlants:ImplicationsforResolvingtheSeedPlantTreeofLife.”American Journal of Botany91(2004):pp.1599–1614.
CameraWireService.“ReallyOldGrowth,PrehistoricPinesFoundinAustralia.”Boulder Daily Camera(1994):1A,8A.
Chase,M.W.“MonocotRelationships:AnOverview.”American Journal of Botany91(2004):pp.1645–1656.
Cowen,R.History of Life.Malden,Mass.:BlackwellPublishing,2005.
Crane,P.R.,P.Herendeen,andE.M.Friis.“FossilsandPlantPhylogeny.”American Journal of Botany91(2004):pp.1683–1699.
Crepet,W.“EarlyBloomers.”Natural History 108(1999):pp.40–41.
Darwin,CharlesR.“LettertoJ.D.Hooker,July22nd1879,”inDarwin,F.andA.C.Seward,(eds.)More Letters of Charles Darwin: A Record of His Work in a Series of Hitherto Unpublished Papers.Vol II.pp.20–21.London,UK:JohnMurray,1903.
Futuyma,D.J.Evolution.Sunderland,Mass.:Sinauer,2005.
Hummel,A.W.“ThePrintedHerbalof1249A.D.”Isis33(1941):pp.439–442.
Judd,W.S.,C.S.Campbell,E.A.Kellogg,P.F.Stevens,andM.J.Donoghue.Plant Systematics A Phylogenetic Approach. 2nd Ed. Sunderland,Mass.:Sinauer,2002.
Klesius,M.“TheBigBloom.”National Geographic 202(2002):pp.102–121.
Levetin,E.,K.McMahon.Plants and Society. 2nd Ed. Boston:WCBMcGraw-Hill,1999.
Lewis,L.A.,R.M.McCourt.“GreenAlgaeandtheOriginofLandPlants.” American Journal of Botany91(2004):pp.1535–1556.
Linnaeus,C.“GeneraPlanatarum.”1787.inBaigrie,B.S.Scientific Revolutions. Primary texts in the History of Science.UpperSaddleRiver,N.J.:PearsonPrenticeHall,2004.
Lutzoni,F.,F.Kauff,C.J.Cox,D.McLaughlin,G.Celio,B.Dentinger,etal.“AssemblingtheFungalTreeofLife:Progress,Classification,andEvolutionofSubcellularTraits.”American Journal of Botany91(2004):pp.1446–1480.
124
Milius,S.“ShouldWeJunkLinnaeus?”Science News156(1999):pp.268–270.
Niklas,K.“What’sSoSpecialAboutFlowers?”Natural History 108(1999):pp.42–45.
Palmer,J.D.,D.E.Soltis,andM.W.Chase.“ThePlantTreeofLife:AnOverviewandSomePointsofView.”American Journal of Botany91(2004):pp.1437–1445.
Pryer,K.M.,E.Schuettpelz,P.G.Wolf,H.Schneider,A.R.Smith,andR.Cranfill.“PhylogenyAndEvolutionOfTheFerns(Monilophytes)WithAFocusOnTheEarlyLeptosporangiateDivergences.”American Journal of Botany91(2004):pp.1582–1598.
Raven,P.H.,G.B.Johnson,J.B.Losos,andS.R.Singer.Biology. 7thEd.NewYork:McGraw-Hill,2005.
Regal,P.J.“EcologyandEvolutionofFloweringPlantDominance.”Science196(1977):pp.622–629.
Rost,T.L.,M.G.Barbour,C.R.Stocking,andT.M.Murphy.Plant Biology. 2ndEd.Toronto,Canada:ThompsonBrooks/Cole,2006.
Sanderson,M.J.,J.L.Thorne,N.Wikstrom,andK.Bremer.“MolecularEvidenceOnPlantDivergenceTimes.”American Journal of Botany91(2004):pp.1656–1665.
Savage,J.M.“SystematicsandtheBiodiversityCrisis.”BioScience45(1995):pp.673–679
Shaw,J.,andK.Renzaglia.“PhylogenyandDiversificationoftheBryophytes.”American Journal of Botany91(2004):pp.1557–1581.
Simpson,B.B.,andJ.Cracraft.“Systematics:TheScienceofBiodiversity.”BioScience 45(1995):pp.670–672
Soltis,P.S.,andD.E.Soltis.“TheOriginandDiversificationofAngiosperms.”American Journal of Botany91(2004):pp.1614–1626.
TreeofLifeWebProject.Availableonlineathttp://tolweb.org/tree/phylogeny.html
Uno,G.,R.Storey,andR.Moore.Principles of Botany. NewYork:McGraw-HillHigherEducation,2001.
USDAPLANTSdatabase.Availableonlineathttp://www.plants.usda.gov
Withgott,J.“IsIt‘SoLongLinnaeus’?”BioScience 50(2000):pp.646–651.
Zimmer,E.A.,Y.-L.Qio,P.K.Endress,andE.M.Friss.“CurrentPerspectivesOnBasalAngiosperms.”International Journal of Plant Sciences161Supplement(2000):S1–S2.
125
Anderson,Edgar.Plants, Man and Life. St.Louis,Mo.:MissouriBotanicalGarden,1997.
Baskin,CarolC.andJerryM.Baskin.Seeds. Ecology, Biogeography, and Evolution of Dormancy and Germination.SanDiego,Calif.:AcademicPress,1998.
Berlin,Brent,DennisE.Breedlove,andPeterH.Raven.“FolkTaxonomiesandBiologicalClassification.”Science154(1966):pp.273–275.
Blackmore,StephenandElizabethTootill,eds.The Facts on File Dictionary of Botany.NewYork:FactsonFile,Inc.,1984.
Durrell,Gerald.A Practical Guide for the Amateur Naturalist.London,U.K.:AlfredA.Knopf,Inc.,1982.
Erickson,Jon.A History of Life on Earth: Understanding Our Planet’s Past.NewYork:FactsonFile,Inc.,1995.
Gould,StevenJ.“Linnaeus’sLuck?”Natural History(2000):pp.18–25,pp.66–69,pp.74–76.
Miller,G.Tyler,Jr.Essentials of Ecology.PacificGrove,Calif.:BrooksCole,2005.
Miller,DouglassR.andAmyY.Rossman.“Systematics,Biodiversity,andAgriculture.”BioScience45(1995):pp.680–686.
Morell,Virginia.“TheVarietyofLife.”National Geographic195(1999):pp.6–31.
Smith,JamesP.,Jr.Vascular Plant Families.Eureka,Calif.:MadRiverPress,Inc.,1977.
Wilson,EdwardO.“Biodiversity:Challenge,Science,Opportunity.”American Zoologist 32(1992):pp.1–7.
Wilson,EdwardO.The Future of Life.NewYork:VintageBooks,2002.
Young,Paul.The Botany Coloring Book.NewYork:HarperCollinsPublishers,1982.
Web SitesAmerican Bryological and Lichenological Society
http://www.unomaha.edu/~abls/
American Fern Societyhttp://amerfernsoc.org
Angiosperm Phylogeny Websitehttp://www.mobot.org/MOBOT/research/APweb/
126
Botanical Society of Americahttp://www.botany.org
Ecological Society of Americahttp://www.esa.org
Flora of North Americahttp://www.fna.org/FNA/
Fungi Onlinehttp://nt.ars-grin.gov/sbmlweb/fungi/index.cfm
Mycological Society of Americahttp://www.msafungi.org
National Biological Information Infrastructurehttp://www.nbii.gov/disciplines/botany/
New York Botanical Garden Herbariumhttp://www.nybg.org/bsci/herb/
Paleobotanical Section of the Botanical Society of Americahttp://www.dartmouth.edu/~daghlian/paleo/
Phylogeny of Life http://www.ucmp.berkeley.edu/exhibit/phylogeny.html
Royal Botanic Gardens, Kewhttp://www.rbgkew.org.uk
Smithsonian National Museum of Natural Historyhttp://www.mnh.si.edu
Wayne’s Word Online Textbook of Natural Historyhttp://waynesword.palomar.edu
page:
127
2-3: IgorKaron/www.shutter stock.com
5: (a)WinthropBrookhouse/ www.shutterstock.com,(b) AleksanderBolbot/www. shutterstock.com,(c)Rodney Mehring/www.shutterstock .com,(d)AnetteLinnea Rasmussen/www.shutter stock.com
14: ©InfobasePublishing 16: ©InfobasePublishing 18-19: MerrylMcNaughton/www.
shutterstock.com 21: GeorgetteDouwma/Photo
Researchers,Inc. 24: LibraryofCongress[LC-
USZ62-11324] 28: ©InfobasePublishing 30: ©ScottCamazine/
PhototakeUSA.com 32-33: MichaelStevens/
Shutterstock.com 35: JoshMeyer/Shutterstock.com 38: (a)ChrisHellyar/
Shutterstock.com,(b)Keith Weller,(c)RomeoMihulic/ www.shutterstock.com,(d) AndreNantel/www.shutter stock.com
39: ©InfobasePublishing 43: IngaSpence/Visuals
Unlimited 48: RobertandJeanPollock/
VisualsUnlimited 50-51: ZavodskovAnatoliy
Nikolaevich/www.shutter stock.com
53: AnneKitzman/www.shutter stock.com
55: Amygdalaimagery/www. shutterstock.com
56: DavidT.Roberts/Natures Images/PhotoResearchers, Inc.
58: KathyMerrifield/Photo Researchers,Inc.
62-63: C.Salisbury/www.shutter stock.com
67: PerennouNuridsany/Photo Researchers,Inc.
69: MichaelP.Gadomski/Photo Researchers,Inc.
72: PeterHansen/www.shutter stock.com
74: ©InfobasePublishing 75: ©JacquesJangoux/Visuals
Unlimited 78-79: TianRencelj/www.shutter
stock.com 80: M.PhilipKahl/Photo
Researchers,Inc. 81: PeterBlazek/www.shutter
stock.com 83: (a)SusanMcKenzie/www.
shutterstock.com,(b) VladimirIvanov/www.shut terstock.com,(c)Chandral Photo/www.shutterstock .com,(d)KathyMerrifield/ PhotoResearchers,Inc.
88: KathyMerrifield/Photo Researchers,Inc.
90: GilbertS.Grant/Photo Researchers,Inc.
94-95: MarkGrenier/www.shutter stock.com
97: ©InfobasePublishing 99: ©InfobasePublishing 103: (a)©Biodisc/Visuals
Unlimited,(b)©Dr. JohnD.Cunningham/ VisualsUnlimited
page:
128
106: (a)JoyFera/www.shutter stock.com,(b)LarryYe/ www.shutterstock.com,(c) LarryYe/www.shutterstock .com,(d)RavshanMirzaitov/ www.shutterstock.com
108: (a)NataliaBratslacasky/ www.shutterstock.com,(b) KeithWeller,(c)StuartElfett/ www.shutterstock.com
Cover:©WizData,Inc./Shutterstock.com(topright);©OoiSzeErh/Shutterstock.com(topleft);©Heng,BoonKiat/Shutterstock.com(bottomleft);©LeniceHarms/Shutterstock.com(bottomright)
129
Abominablemystery,96Adanson,Michel,23Adder’stongueferns,71AgeofHerbals,20–21Airpollution,49Algae
brown,46–47evolutionand,12,34,45,46,52green,12,44–46lichensand,47–48withmossinname,59mutualisticrelationshipwithfungi,
45red,46,47studyof,44valueof,34
Allergies,34,89Amborellaceae,109–110Amentiferae,109Anatomy,29,35–36AngiospermPhylogenyGroup,26Angiosperms
dominantgenerationin,15evolutionof,29,109–111featuresof,96–99firstappearanceof,96lifecycleof,98,100–101,111majorgroupsof,101–105withmossinname,59relationshiptognetophytesof,91symbolismofspecific,96valueof,105–109,110–111
AnimaliaKingdom,12mutualisticrelationshipwithalgae,45relationshipoffungito,12
Antheridiaofbryophytes,54,56,57,58ofseedlessvascularplants,67,68
Araucariaceae,87Arbuscularmycorrhizalfungi,37,39,
40–41ArchaeaKingdom,12Archaeopteris,91
Archegoniaofbryophytes,54,56,57,58ofgymnosperms,85ofseedlessvascularplants,67
Artificialclassificationsystem,23Arums,101Ascomycota,37,39,41–42,47–48Asexualreproduction,36,40,57,76Asteraceae,107Autotrophs,13
BacteriaKingdom,12,106Basalangiosperms,102,109–110Basidiomycota,37,39,42–43,47Beans,105–106Bennettitales,92Binomialnomenclature,7–8,23Bock,Hieronymus,21Brackenferns,73Bracts,91Breadmold,40Bristleconepines,84Brown,Robert,81Brownalgae,46–47Brunfels,Otto,21Bryophytes
ancestorsof,52dominantgenerationin,15evolutionof,29,60–61featuresof,52,54lifecycleof,54,56,66,67–68majorgroupsof,52,54,56–59sporophytesof,66valueof,61
Burns,Robert,96
Calamites,70–71,92Carotenoids,13Carrageenan,34Cellwalls,13
cuticlesand,52offungi,35ofseedlessvascularplants,65–66
130
Charophytes,45–46Cheng Lei Pen Ts’ao(TheMaterials
ofMedicineArrangedAccordingtoPattern,TangShen-wei),20
Chestnutblight,41Chi’enNung(emperorofancient
China),20China,ancient,20Chitin,35Chlorophylls,13Chlorophytes,45Chloroplasts,13Chytrids,37,39,40Cibo,Gherhards,22Clades
ofangiosperms,103–104ofbryophytes,57classificationand,27ofseedlessvascularplants,64,76
Cladistics,26–29Classification,10–11,22–23,25–26,29Clubfungi,37,39,42–43Clubmosses,69–70,77Coal,64Conescales,82,85Cones
ofclubmosses,70ofcycadeoids,92ofcycads,87ofginkgos,88,89ofgnetophytes,91ofgymnosperms,82ofpines,84,85ofWelwitschia mirabilis,80
Conifers,85–87Cordaites,92Coreangiosperms,102–104Corms,70Cotyledons,101–102Croziers,72Crutoselichens,49Cupressaceae,86–87Cuticles,52
Cyanobacteria,47–48,73Cycadeoids,92Cycads(Cycadophyta),87,92
Darwin,Charles,25,26,96Dawnredwoods,89DeJussieu,AntoineLaurent,23,25De Materia Medica(TheMaterialof
Medicine,Dioscorides),20Deciduoustrees,84Decomposers,36,40,43Dendrograms,11,27Dichotomouskeys,29Dicots,101–104Dikaryoticcells,36–37Dioscorides,20,23Diversity
ofangiosperms,96–97valueof,4,6
DoctrineofSignatures,57Doublefertilization,101
Eberspapyrus,20Ecologicalsystems
algaeand,34,44decomposersand,36,40,43functioningof,6successionof,61
Egypt,ancient,20Endosperm,101,111Energyconversion.SeephotosynthesisEngler,109Ephedras,89Epiphytes,109Equisetales,70–71Ethnobotany,6Eudicots,104–105,107,109,110Eukaryoticorganisms,12Evergreens,84Evolution
algaeand,12,34,45,46,52ofangiosperms,29,109–111ofbryophytes,29,60–61
131
cladisticsand,26–29Darwiniantheoryof,25,26offungi,34,39,40geologicaltimescaleofplants,60ginkgosand,88ofgymnosperms,29,91–92heterosporyand,68ofroots,69ofseedlessvascularplants,29,64,
66,76ofseedsandpollen,82stomataand,58Seealsophylogeny
Fabaceae,105–106Families,9,10Ferns,70–74,76Fiddleheads,72,73,77Fieldguides,29Filicales,73–74,76Five-merousflowers,105Flagella,40Flavonoids,46Floras,29Floweringplants.SeeangiospermsFolioselichens,49Food
algaeas,34angiospermsas,105–107,109,
110–111fungias,42gymnospermsas,93seedlessvascularplantsas,77
Four-merousflowers,105Fronds,66,73Fruits,110–111Fruticoselichens,49Fuchs,Leonart,21Fungi
anatomyof,35–36dangersof,34,42–43evolutionof,34,39,40lichensand,47–48
lifecycleof,36–37,40,41–42majorgroupsof,37,39–43membersof,12mutualisticrelationshipwithalgae,
45valueof,34,36,42
Gametes,14,15,98Gametophytes
ofangiosperms,100ofbryophytes,54,56,57,59,67–68described,15ofgymnosperms,84ofseedlessvascularplants,66,67–68
Gemmae,57Generations,alternate,15,54,66Genusnames,8,10,23Ghini,Luca,21–22Giantrafflesia,110Giantsequoias,84Ginkgos,87–89,92Glomeromycota,37,39,40–41Gnetophytes,89,91Granitemosses,59Grasses,107Greece,ancient,20Greenalgae,12,44–46Gymnosperms
evolutionof,29,91–92featuresof,82,84lifecycleof,82,84–85majorgroupsof,82,85–89,91seedsof,80–81valueof,87,93
Hallucinogens,43Herbalmedicines,6,57Herbaria,22Herbariumsheets,22Herbs,107Heterospory,68Heterotrophs,12,36
Seealsofungi
132
Historia Naturalis(NaturalHistory,PlinytheElder),20
Historia Plantarum(HistoryofPlants,Theophrastus),20
Homeopathicmedicine,57Homospory,67–68,73Honeymushrooms,36Hornworts,58,61Horsetails,70–71Hunter-gatherers,4Hydroids,59Hyphae,35–36Hypotheses,93
Identificationguides,29Illiciales,109–110Inflorescences,98–99,110InternationalBotanicalCongresses,
9–10InternationalCodeofBotanical
Nomenclature(ICBN),8–10,11Iridaceae,108–109Isotales,70
Kaempfer,Engelbert,89Kelp,47Kingdoms
definitionof,10different,11–13
Landscaping,93“TheLanguageofFlowers,”96Latin,8Leaves
cotyledonsofangiosperms,101–102evolutionof,66oflycophytes,68ofmarattoidferns,71–72ofmonilophytes,70ofophioglossoidferns,71ofseedlessvascularplants,69ofwaterferns,73ofWelwitschia mirabilis,80
Legumes,105–106Lepidodendrontrees,64Leptoids,59Lichens,47–49,59Lifecycles
alternationofgenerations,15ofangiosperms,98,100–101,111ofbryophytes,54,56,66,67–68offungi,36–37,40,41–42ofgreenalgae,44–45ofgymnosperms,82,84–85lengthof,4ofseedlessvascularplants,66,67–68
Liliaceae,108,109Liliopsida,101,104–105Linnaeus,Carolus,7–8,23Liverworts,57,60–61Lycophytes,64,68–70,92
Magnol,Pierre,22,23Magnoliaceae,109Magnoliids,103–104,110Magnoliopsida,101–104Marattoidferns,71–72Marsileales,73The Material of Medicine(Dioscorides),
20The Materials of Medicine Arranged
According to Pattern(TangShen-wei),20
MedicineDoctrineofSignaturesand,57fungias,34,42gymnospermsas,89herbal,6,57mossesas,61prescriptiondrugs,6
Megaphylls,70Megaspores,68Meiosis
ofchytrids,40ofclubfungi,42described,15
133
ofgreenalgae,45ofgymnosperms,84–85ofsacfungi,42
Microspores,68Mitosis,15,85Modernclassificationsystem,26Molds,34Monilophytes,64,70–74,76Monkeypuzzletrees,87Monocots,101,104–105,107,108,110Monophyleticgroups,27,89Morphology,29Mosses,56,58–59,61Mushrooms,42–43Mutualism,41,45,47–48Myceliaoffungi,35–37,41–42Mycorrhizae,41Mycorrhizalfungi,69
Nakedseedplants.SeegymnospermsNames/naming.SeetaxonomyNamibDesert,80Narcotics,107Naturalclassificationsystem,25Natural History(PlinytheElder),20Naturalselection,25Navalstores,93Nonfloweringseedplants.See
gymnospermsNorfolkIslandpines,87Nuclei,12,36–37Nymphaeaceae,109–110
Ophioglossoidferns(ophioglossales),71
Orchidaceae,109Orchids,101Orders,11Organelles,12The Origin of Species(Darwin),25Ornamentation,87,93,105,107,
108–109Ovules
ofangiosperms,97–98,100ofgymnosperms,85
Paleobotanists,89Parasiticplants,13Peatmosses,59,61Penicillin,34,42Petals,roleof,98Pharmaceuticalindustry,6Phloem,82,84Photoautotrophs,13Photosynthesis
described,13redalgaeand,47sporophytesofhornworts,58valueof,6
Phycobilins,47Phycology,44Phylocode,31Phylogeny,10,26–29,93
SeealsoevolutionPigments,46,47
SeealsophotosynthesisPinaceae,85–86Pines,84–86,93PlantaeKingdom,13Plants,definingtraitsof,13–14PlinytheElder,20Podocarpaceae,87Poisons,34,42–43,107Pollen
ofangiosperms,98,100,101,104,110–111
evolutionof,82ofgymnosperms,85,87,88,91
Polynomialnomenclature,7,22–23Prantl,109Prasinophytes,45Prescriptiondrugs,6Printingpress,20–21Prokaryoticorganisms,12ProtistaKingdom,12Protists,37,47
134
Protogymnosperms,91Protonemas,54,56Psilotales,70–71Puffballs,42
Quillworts,70
Ranunculaceae,109Ray,John,22,101Redalgae,46,47Redtides,47Redwoodtrees,84Religiousceremonies,4,43Reproduction.SeelifecyclesRespiratoryillnesses,34,89Resurrectionplants,69Rhizoids,54,56Rome,ancient,20Roots,66,69,70Rosaceae,105Roses,105Rusts,43
Sacfungi,37,39,41–42Salviniales,73Seedferns,91,92Seedlessnonvascularplants.See
BryophytesSeedlessvascularplants
evolutionof,29,64,66,76featuresof,65–66lifecycleof,66,67–68majorgroupsof,64–65,68–74,76withmossinname,59valueof,76–77
Seedsofangiosperms,98,101evolutionof,82naked,80–81valueof,82
Sepals,98Seta,59Sexualreproduction,40,41–42,44–45,
56Shelffungi,43Sloths,45Smuts,43Sori,74Spadixes,110Species
abbreviationsfor,11ofalgae,45,46,47ofangiosperms,96,109ofbryophytes,52,56,57,58,59definitionof,10–11offungi,37,40ofgymnosperms,82,85,86,87,89identifyingname,8inPlantaeKingdom,13ofseedlessvascularplants,68,69,70,
71,73Species Plantarum(Linnaeus),23Sphagnummoss,61Spikemosses,69Sporangia
ofgymnosperms,84ofseedlessvascularplants,66,67,
68–69,70–71,73–74Spores
asexualreproductionof,36,40,57ofgymnosperms,84–85ofseedlessvascularplants,67sexualreproductionof,40,41–42,
44–45,56Sporophylls,68–69,70Sporophytes
ofangiosperms,100,101ofbryophytes,54,56,57,58,59described,15ofgymnosperms,84ofseedlessvascularplants,66,67,69
Sterilejackets,14Stomataofhornworts,58Stoneworts,46Strobili,70,80Sunflowers,107
135
Symbioticrelationships,34,69,106Systematics
classification,10–11dataused,29,31early,22–23,25hypothesesin,93phylogeny,10taxonomy,7–11,31,57
TangShen-wei,20Taxa,11Taxonomy
abbreviationsand,11binomialsystem,7–8commonplantnames,7DoctrineofSignaturesand,57ICBNrules,8–10,11levelsof,10Phylocodesystem,31
Tepals,98Thallus,57,58Theophrastus,20Theory,described,26
Three-merousflowers,105Toadstools,42Tracheids,65Tracheophytes,65TreeofLifeProject,26Trees,64,84,105Tribalpeoples,6Trimeniaceae,109–110Trueferns,73–74,76Truemosses,59
Vascularplants,65Vegetativereproduction,57
Waterferns,73Welwitschia mirabilis,80,89Whiskferns,70–71Whorlsofflowers,98,105
Xylem,82,84
Zygomycetes,37,39,40Zygospores,40
136
J. Phil Gibson holds degrees in botany from Oklahoma State University(B.S.)andtheUniversityofGeorgia(M.S.),andaPh.D. inenvironmen-tal population and organismic biology from the University of Colorado.He is currently an associate professor in the Department of Botanyand Microbiology and the Department of Zoology at the University ofOklahoma. His research investigates the ecology and evolution of plantreproductivesystems.Healsoconductsconservation-focusedresearchontreespecies.Hehaspublishedavarietyofresearchpapersandpresentedhis work at scientific conferences. Gibson is a member of the ProjectKaleidoscopeFacultyforthe21stCenturyinrecognitionofhiseffortstoimprove undergraduate science education. He is also an active memberof theBotanicalSocietyofAmericaandtheAssociationofSoutheasternBiologists.
terri r. Gibsonholdsabachelor’sdegreeinzoologyfromtheUniversityofGeorgia.Shehasworkedasascientificillustratorandalsoasaresearchassistant studying, among other things, plant population genetics, plantmorphology,andhumanimmunodeficiencyvirus(HIV).Sheiscurrentlypursuingacareerinchildren’sliterature.