Ch 29 Plant Diversity - philipdarrenjones.com

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Plant Diversity BIOL 221

Ch. 29

Overview: The Greening of Earth •  First 3 billion years of Earth’s history

•  The terrestrial surface was lifeless

•  Since colonizing land

•  plants have diversified into roughly

290,000 living species

ANCESTRAL ALGA

Red algae

Chlorophytes

Charophytes

Embryophytes

Viridiplantae Streptophyta

Plantae

Land plants evolved from green algae •  Green algae called charophytes

•  are the closest relaIves of land plants

•  Comparisons of both nuclear and chloroplast genes

•  point to charophytes as the closest living relaIves of land plants

•  Note

•  that land plants are not descended from modern charophytes

•  but share a common ancestor with modern charophytes

2

Morphological and Molecular Evidence •  Many characterisIcs of land plants

•  also appear in a variety of algal clades

•  land plants share four key traits only with charophytes:

1.  Rose-‐shaped complexes for cellulose synthesis

2.  Peroxisome enzymes

3.  Structure of flagellated sperm

4.  FormaIon of a phragmoplast

Adapta@ons Enabling the Move to Land •  Sporopollenin

•  In charophytes

•  polymer that prevents exposed zygotes from drying

out

•  Movement onto land

•  Provided: unfiltered sun, more plenIful CO2, nutrient-‐rich soil,

and few (any?) herbivores or pathogens

•  Challenges: a scarcity of water and lack of structural support

Morphological and Molecular Evidence

ANCESTRAL ALGA

Red algae

Chlorophytes

Charophytes

Embryophytes

Viridiplantae

Streptophyta

Plantae

•  The accumulaIon of traits that facilitated survival on land

•  may have opened way to colonizaIon by plants

•  SystemaIsts debaIng the boundaries of the plant kingdom

•  Some think the plant kingdom should be expanded

•  to include some or all green algae

•  UnIl resoluIon

•  we will retain the embryophyte definiIon of kingdom Plantae

3

Derived Traits of Plants •  Four key traits appear in nearly all land plants

•  but are absent in the charophytes:

1.  AlternaIon of generaIons

•  with mulIcellular, dependent embryos

2.  Walled spores produced in sporangia

3.  MulIcellular gametangia

4.  Apical meristems

Embryo Maternal tissue

Wall ingrowths

Placental transfer cell (outlined in blue)

Embryo (LM) and placental transfer cell (TEM) of Marchantia (a liverwort)

2 µm

10 µm

•  alterna@on of genera@ons

•  Plants alternate between two stages

•  Gametophyte -‐ haploid

•  produces haploid gametes by mitosis

•  Sporophyte – diploid

•  from fusion of the gametes

•  produces haploid spores by meiosis

•  diploid embryo (zygote)

•  retained within female gametophyte (haploid)

•  placental transfer cells

•  Transfer nutrients from parent to embryo

•  Extra surface area for exchange

•  Embryophytes

•  Land plants because of the dependency of the embryo on the parent

Derived Traits of Plants Gametophyte (n)

Gamete from another plant

n

n

Mitosis

Gamete

FERTILIZATION MEIOSIS

Mitosis

Spore n n

2n Zygote

Mitosis

Sporophyte (2n)

Alternation of generations

Walled Spores Produced in Sporangia

•  Sporangia

•  Organ on sporophyte that produces spores

•  Sporocytes

•  Diploid cells in sporangia

•  undergo meiosis to generate

haploid spores

•  contain sporopollenin

Spores Sporangium

Sporophyte

Longitudinal section of Sphagnum sporangium (LM)

Gametophyte

Sporophytes and sporangia of Sphagnum (a moss)

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Mul@cellular Gametangia

•  Gametangia

•  Produce gametes

•  Archegonia

•  Female gametangia

•  produce eggs and are the site of ferIlizaIon

•  Antheridia

•  Male gametangia

•  site of sperm producIon and release

Female gametophyte

Male gametophyte

Antheridium with sperm

Archegonium with egg

Archegonia and antheridia of Marchantia (a liverwort)

Apical Meristems •  Apical meristems

•  Used by plants to sustain conInual growth

•  Cells differenIate into various Issues

Apical meristem of shoot

Developing leaves

Apical meristems

Apical meristem of root Root 100 µm 100 µm Shoot

The Origin and Diversifica@on of Plants •  Fossil evidence

•  indicates that plants were on land

•  at least 475 million years ago

•  Fossilized spores and Issues

•  have been extracted from 475-‐million-‐year-‐old rocks

(a) Fossilized spores

(b) Fossilized sporophyte tissue

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•  Land plants can be informally grouped

•  Based on the presence or absence of vascular @ssue

•  Vascular plants

•  Have vascular Issue

•  Most plants

•  Bryophytes

•  Nonvascular plants

The Origin and Diversifica@on of Plants

Origin of land plants (about 475 mya) 1 2 3

1

2

3

Origin of vascular plants (about 420 mya) Origin of extant seed plants (about 305 mya)

ANCES- TRAL GREEN ALGA

Liverworts

Hornworts

Mosses

Lycophytes (club mosses, spike mosses, quillworts)

Pterophytes (ferns, horsetails, whisk ferns)

Gymnosperms

Angiosperms

Seed plants Seedless vascular plants

Nonvascular

plants (bryophytes)

Land plants Vascular plants

Millions of years ago (mya) 500 450 400 350 300 50 0

•  Seedless vascular plants

•  Can be divided into clades

–  Lycophytes

–  club mosses and their relaIves

–  Pterophytes

–  ferns and their relaIves

–  Seedless vascular plants are paraphyleIc

–  And are of the same level of biological organizaIon



1

2

3



Liverworts

Hornworts

Mosses



Gymnosperms

Angiosperms


Nonvascular

plants (bryophytes)



•  Seed

•  an embryo and nutrients surrounded by a protecIve coat

•  Seed plants form a clade

•  and can be divided into further clades:

–  Gymnosperms

–  “naked seed” plants, including the conifers

–  Angiosperms

–  flowering plants



1

2

3



Liverworts

Hornworts

Mosses



Gymnosperms

Angiosperms


Nonvascular

plants (bryophytes)



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Bryophyte life cycles dominated by gametophytes •  Bryophytes

•  represented today by three phyla of small herbaceous (nonwoody) plants

–  Liverworts, phylum Hepatophyta

–  Hornworts, phylum Anthocerophyta

– Mosses, phylum Bryophyta

•  Mosses are most closely related to vascular plants

Bryophyte Gametophytes

•  In all three bryophyte phyla

•  gametophytes are larger and longer-‐living than sporophytes

•  Sporophytes

•  typically present only part of the Ime

Fig. 29-‐8-‐1

Key Haploid (n) Diploid (2n) Protonemata

(n)

“Bud”

“Bud”

Male gametophyte (n)

Female gametophyte (n)

Gametophore

Rhizoid

Spores

Spore dispersal

Peristome

Sporangium MEIOSIS Seta

Capsule (sporangium)

Foot

Mature sporophytes

Capsule with peristome (SEM)

Female gametophytes

2 m

m

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Fig. 29-‐8-‐2


(n)

“Bud”

“Bud”



Gametophore

Rhizoid

Spores

Spore dispersal

Peristome



Foot

Mature sporophytes


Female gametophytes

2 m

m

Raindrop

Sperm

Antheridia

Egg

Archegonia

FERTILIZATION (within archegonium)

Fig. 29-‐8-‐3


(n)

“Bud”

“Bud”



Gametophore

Rhizoid

Spores

Spore dispersal

Peristome



Foot

Mature sporophytes


Female gametophytes

2 m

m

Raindrop

Sperm

Antheridia

Egg

Archegonia


Zygote (2n)

Embryo

Archegonium

Young sporophyte (2n)

•  A spore germinates into a gametophyte

•  composed of a protonema and gamete-‐producing gametophore

•  Rhizoids

•  Anchor gametophytes to substrate

•  Lack of vascular Issues restricts the height of gametophytes


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•  Mature gametophytes

•  produce flagellated sperm in antheridia and

an egg in each

archegonium

•  Sperm swim through a film

of water to reach and

ferIlize the egg



(n)

“Bud”

“Bud”



Gametophore

Rhizoid

Spores

Spore dispersal

Peristome



Foot

Mature sporophytes


Female gametophytes

2 m

m

Raindrop

Sperm

Antheridia

Egg

Archegonia


Zygote (2n)

Embryo

Archegonium


Bryophyte Sporophytes •  Bryophyte sporophytes

•  grow out of archegonia

•  smallest and simplest sporophytes

•  of all extant plant groups

•  consists of a foot, a seta (stalk), and a sporangium,

•  also called a capsule

•  which discharges spores through a peristome

•  Hornwort and moss sporophytes have stomata for gas exchange


(n)

“Bud”

“Bud”



Gametophore

Rhizoid

Spores Spore dispersal

Peristome



Foot Mature sporophytes


Female gametophytes

2 m

m

Raindrop

Sperm

Antheridia

Egg

Archegonia


Zygote (2n)

Embryo

Archegonium


Thallus Gametophore of female gametophyte

Marchantia polymorpha, a “thalloid” liverwort

Marchantia sporophyte (LM)

Sporophyte

Foot Seta


500 µm

Plagiochila deltoidea, a “leafy” liverwort

An Anthoceros hornwort species

Sporophyte

Gametophyte

Gametophyte

Seta

Capsule Sporophyte (a sturdy plant that takes months to grow)

Polytrichum commune, hairy-cap moss

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Ferns and other seedless vascular plants •  Bryophytes and bryophyte-‐like

plants

•  Dominated first 100 million years of plant evoluIon

•  Vascular plants

•  began to diversify during the Devonian and Carboniferous periods

•  Vascular Issue

•  allowed these plants to grow tall

•  Seedless vascular plants

•  have flagellated sperm and are usually restricted to moist environments


1

2

3



Liverworts

Hornworts

Mosses



Gymnosperms

Angiosperms


Nonvascular

plants (bryophytes)



Origins and Traits of Vascular Plants •  Fossils of the forerunners of vascular

plants

•  date back about 420 million years

•  These early Iny plants had independent, branching sporophytes

•  Living vascular plants are characterized by:

•  Life cycles with dominant sporophytes

•  Vascular Issues called xylem and phloem

•  Well-‐developed roots and leaves

Life Cycles with Dominant Sporophytes •  In contrast with

bryophytes…

•  sporophytes of seedless vascular

plants are the larger

generaIon

•  as in the fern

•  …gametophytes

•  are just Iny plants that grow on or below the

soil surface

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Fig. 29-‐13-‐1

Key

Haploid (n) Diploid (2n)

MEIOSIS Spore dispersal

Sporangium

Sporangium Mature sporophyte (2n)

Sorus

Fiddlehead

Fig. 29-‐13-‐2

Key



Sporangium


Sorus

Fiddlehead

Spore (n)

Young gametophyte

Mature gametophyte (n) Archegonium

Egg

Antheridium

Sperm

FERTILIZATION

Fig. 29-‐13-‐3

Key



Sporangium


Sorus

Fiddlehead

Spore (n)

Young gametophyte

Mature gametophyte (n) Archegonium

Egg

Antheridium

Sperm

FERTILIZATION New sporophyte

Gametophyte

Zygote (2n)

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Transport in Xylem and Phloem •  Vascular plants have two types of

vascular Issue:

•  xylem and phloem

•  Xylem

•  conducts most of the water and minerals

•  includes dead cells called tracheids

•  strengthened by lignin and provide structural support

•  Phloem

•  Moves sugars, amino acids, and other organic products

•  consists of living cells

Evolu@on of Roots •  Roots

•  Organs that anchor vascular plants

•  enable vascular plants to absorb water

•  and nutrients from the soil

•  And deliver those nutrients up a taller/larger plant

•  May have evolved from subterranean stems

•  Organs that increase the surface area for capturing light

•  Leaves are categorized by two types:

–  Microphylls

–  leaves with a single vein

–  Megaphylls

–  leaves with a highly branched vascular system

•  According to the fossil record

•  microphylls evolved first (410 vs. 370 mya)

•  as outgrowths of stems

Evolu@on of Leaves

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Sporophylls and Spore Varia@ons

•  Sporophylls

•  modified leaves with sporangia

•  Sori

•  clusters of sporangia on the undersides of sporophylls

•  Strobili

•  cone-‐like structures formed from

groups of sporophylls

•  homosporous

•  produce one type of spore that develops into a bisexual gametophyte

•  Most seedless vascular plants -‐ ferns

•  heterosporous

•  produce megaspores that give rise to female gametophytes

•  and microspores that give rise to male gametophytes

•  All seed plants and some seedless vascular plants

Sporophylls and Spore Varia@ons

Homosporous spore production

Sporangium on sporophyll

Single type of spore

Typically a bisexual gametophyte

Eggs

Sperm

Eggs

Sperm

Heterosporous spore production

Megasporangium on megasporophyll Megaspore Female

gametophyte

Male gametophyte

Microspore Microsporangium on microsporophyll

Classifica@on of Seedless Vascular Plants •  There are two phyla of seedless vascular plants:

–  Phylum Lycophyta

–  includes club mosses, spike mosses, and quillworts

–  Phylum Pterophyta

–  includes ferns, horsetails, and whisk ferns and their relaIves Lycophytes (Phylum Lycophyta)

Selaginella apoda, a spike moss

Isoetes gunnii, a quillwort

Strobili (clusters of sporophylls)

2.5 cm

Diphasiastrum tristachyum, a club moss 1 cm

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Fig. 29-‐15e

Pterophytes (Phylum Pterophyta) Athyrium filix-femina, lady fern

Vegetative stem

Strobilus on fertile stem

1.5

cm

25 c

m

2.5

cm

Psilotum nudum, a whisk fern

Equisetum arvense, field horsetail

Phylum Lycophyta:

•  Giant lycophytes

•  thrived for millions of years in moist

swamps

•  Surviving species are small herbaceous

plants

•  Club mosses and spike mosses have

vascular Issues

•  and are not true mosses

Phylum Lycophyta: •  Ferns

•  most diverse seedless vascular plants

•  more than 12,000 species

•  Horsetails

•  diverse during the Carboniferous period

•  now restricted to the genus Equisetum

•  Whisk ferns

•  resemble ancestral vascular plants

•  but are closely related to modern ferns

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The Significance of Seedless Vascular Plants •  Ancestors of modern lycophytes, horsetails,

and ferns

•  grew to great heights during the Devonian and Carboniferous

•  forming the first forests

•  Increased photosynthesis

•  may have helped produce the global cooling

•  at the end of the Carboniferous period

•  The decaying plants of these Carboniferous forests eventually became coal

You should now be able to:

1.  Describe four shared characterisIcs and four disInct characterisIcs between charophytes and land plants

2.  DisInguish between the phylum Bryophyta and bryophytes

3.  Diagram and label the life cycle of a bryophyte

4.  Explain why most bryophytes grow close to the ground and are restricted to periodically moist environments

5.  Describe three traits that characterize modern vascular plants and explain how these traits have contributed to success on land

6.  Explain how vascular plants differ from bryophytes

7.  DisInguish between the following pairs of terms: microphyll and megaphyll; homosporous and heterosporous

8.  Diagram and label the life cycle of a seedless vascular plant

Ch 29 Plant Diversity - philipdarrenjones.com

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