The Seedless Vascular Plants: Ferns and Their Relatives

Chapter 21

Outline Introduction Phylum Psilotophyta – The Whisk Ferns Phylum Lycophyta – The Ground Pines, Spike

Mosses and Quillworts Phylum Equisetophyta – The Horsetails and

Scouring Rushes Phylum Polypodiophyta – The Ferns

Introduction During early stages of vascular plant evolution:• Internal conducting tissue developed• True leaves appeared• Roots functioning in absorption and anchorage

developed• Gametophytes became progressively smaller

4 phyla of seedless vascular plants: Psilotophyta, Lycophyta, Equisetophyta, Polypodiophyta

Introduction Psilotophyta• Sporophytes without true

leaves or roots• Stems and rhizomes fork

evenly

Lycophyta• Plants covered with

microphylls - leaves with single vein whose trace not associated with leaf gap

Psilotum

Lycopodium

Introduction Equisetophyta• Sporophytes with ribbed

stems containing silica• Whorled, scalelike

microphylls lacking chlorophyll

Polypodiophyta• Sporophytes with megaphylls

- leaves with >1 vein and leaf trace associated with leaf gap Often large and divided

Equisetum

A fern

Phylum Psilotophyta – The Whisk Ferns

Resemble small, green whisk brooms

Structure and form:• Sporophytes: −Dichotomously forking

stems Above ground stems

arise from rhizomes−Lack leaves and roots

Phylum Psilotophyta – The Whisk Ferns

Structure and form cont’d.:• Sporophytes: −Enations - tiny, green,

superficially leaflike, veinless, photosynthetic flaps of tissue

−Roots, aided by mycorrhizal fungi, scattered along rhizomes

Phylum Psilotophyta – The Whisk Ferns Reproduction:• Sporangia fused in 3s and produced at tips of short

branches• Gametophytes develop from spores beneath ground

−Branch dichotomously−No chlorophyll−Rhizoids aided by mycorrhizal fungi−Archegonia and antheridia scattered on surface

• Zygote develops foot and rhizome• Rhizome separates from foot

Phylum Psilotophyta – The Whisk Ferns

Reproduction cont’d.:

Phylum Psilotophyta – The Whisk Ferns Fossil whisk fern look-alikes• Silurian, 400 mya

−Cooksonia and Rhynia Naked stems and terminal sporangia

• Devonian, 400-350 mya−Zosterophyllum

Naked stems and rounded sporangia along stem Thought to be ancestral to club mosses

Phylum Lycophyta – The Ground Pines, Spike Mosses, and Quillworts

Collectively called club mosses• 2 living major genera

−Lycopodium−Selaginella

• 2 living minor genera• Several genera became extinct about 270 mya

Sporophytes have microphylls

Have true roots and stems

Phylum Lycophyta Lycopodium - ground

pines• Often grow on forest

floors• Stems simple or

branched−Develop from

branching rhizomes• Leaves usually < 1 cm

long• Roots develop along

rhizomes

Phylum Lycophyta

• Sporangia in axils of sporophylls - sporangium-bearing leaves− Some species have

sporophylls with no chlorophyll, are smaller than other leaves and clustered into strobili (singular: strobus)

• In sporangia, sporocytes undergo meiosis, producing spores

Lycopodium reproduction:

Phylum Lycophyta Lycopodium

reproduction cont’d.:

Gametophyte

Phylum Lycophyta Selaginella - spike mosses• Abundant in tropics• Branch more freely than ground pines• Leaves with ligule on upper surface

Phylum Lycophyta Selaginella reproduction:• Produce 2 different kinds of gametophytes =

heterospory−Microsporophylls bear microsporangia containing

microsporocytes, producing tiny microspores - becomes male gametophyte, consisting of antheridium within microspore wall

−Megasporophylls bear megasporangia containing megasporocytes, producing 4 large megaspores -develops into female gametophyte consisting of many cells inside megaspore Several archegonia produced where spore wall

ruptures

Phylum Lycophyta

Selaginella reproduction cont’d.:

Phylum Lycophyta Isoetes - quillworts• Found in areas partially submerged in H2O for part of

year• Microphylls arranged in tight spiral on stubby stem

• Ligules occur towards leaf bases

• Corms have vascular cambium

• Plants generally > 10 cm tall

Phylum Lycophyta Isoetes

reproduction:• Similar to spike

mosses, except no strobili

• Sporangia at bases of leaves

Phylum Lycophyta Ancient relatives of club

mosses and quillworts:• Dominant members of

forests and swamps of Carboniferous, 325 mya−Large, tree-like, up

to 30 meters tall - Lepidodendron

Surface of Lepidodendron, showing microphyll bases

Phylum Equisetophyta – The Horsetails and Scouring Rushes

Equisetum Branched and unbranched

forms, usually > 1.3 m tall Stems jointed and ribbed• If branched, branches in

whorls• Scalelike leaves in whorls at

nodes• Stomata in grooves

between ribs

Phylum Equisetophyta Stem anatomy:• Hollow central cavity from break down of pith

• Two cylinders of smaller canals outside pith− Carinal canals - conduct H2O with xylem and

phloem to outside− Vallecular canals - outside carinal canals contain

air

• Silica deposits on walls of stem epidermal cells

Phylum Equisetophyta

Phylum Equisetophyta Equisetum reproduction:• Asexual by fragmentation of

rhizomes• Sexual reproduction:

−Strobili at tips of stems with sporangia connected to sporangiophores

−Spores green with 4 elaters attached

−Gametophytes lobed, green, cushion-like, up to 8 mm in diameter Spores with

elaters

Phylum Equisetophyta

Equisetum reproduction cont’d.:

Phylum Equisetophyta Ancient relatives of horsetails:• Flourished in Carboniferous, 300

mya

Human and ecological relevance:• Many giant horsetails used for food

by humans and other animals• Scouring rush stems used for

scouring and sharpening

Reconstruction of fossil giant horsetail, Calamites

Phylum Polypodiophyta – The Ferns Structure and form:• Vary in size from tiny floating forms < 1 cm to giant

tropical tree ferns up to 25 m tall−Fern leaves are megaphylls - fronds

Typically divided into smaller segments−Require external H2O for reproduction

Phylum Polypodiophyta – The Ferns Reproduction:• Sporophyte conspicuous

phase−Fronds, rhizomes,

roots−Fronds first appear

coiled in crozier, and unroll and expand Fronds divided

into segments called pinnae (singular: pinna)

Crozier

Phylum Polypodiophyta – The Ferns Reproduction cont’d.:• Sporangia stalked

−Scattered on lower leaf surface, confined to margins, or found in discrete clusters called sori (singular: sorus) Sori may be protected

by indusia (singular: indusium)

−With row of heavy-walled, brownish cells = annulus

Sorus covered by indusium

Phylum Polypodiophyta – The Ferns Reproduction cont’d.:• Meiosis forms spores in sporangia• Spores released and grow into gametophytes called

prothalli (singular: prothallus)• Prothalli one cell thick,

and have archegonia and antheridia

• Zygote develops into young sporophyte

• Gametophyte dies and leaves sporophyte growing independently

Phylum Polypodiophyta – The Ferns

Reproduction cont’d.:

Phylum Polypodiophyta – The Ferns

Fossil relatives of ferns:• Devonian, 375 mya

- possible ancestors of ferns– Resemble ferns

in growth habit, but look more like whisk ferns

Possible ancestors: Aglaophyton and Psilophyton

Phylum Polypodiophyta – The Ferns Fossil relatives of ferns cont’d.• Carboniferous, 320-250

mya - tree ferns abundant−Seeds found on some of

fossil tree ferns

Phylum Polypodiophyta Human and ecological relevance:• House plants

−Function well as air filters• Outdoor ornamentals• Cooked rhizomes as food• Folk medicine• Fronds used in thatching for houses.• Basketry and weaving

Review Introduction Phylum Psilotophyta – The Whisk Ferns Phylum Lycophyta – The Ground Pines, Spike

Mosses and Quillworts Phylum Equisetophyta – The Horsetails and

Scouring Rushes Phylum Polypodiophyta – The Ferns