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
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