The Seedless Vascular Plants:
Ferns and Their Relatives
Chapter 21
Outline
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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
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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
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4 phyla of seedless vascular plants: Psilotophyta,
Lycophyta, Equisetophyta, Polypodiophyta
Introduction
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Psilotophyta
• Sporophytes without true
leaves or roots
• Stems and rhizomes fork
evenly
Psilotum
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Lycophyta
• Plants covered with
microphylls - leaves with
single vein whose trace not
associated with leaf gap
Lycopodium
Introduction
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Equisetophyta
• Sporophytes with ribbed
stems containing silica
• Whorled, scalelike
microphylls lacking
chlorophyll
Equisetum
Polypodiophyta
• Sporophytes with megaphylls
- leaves with >1 vein and leaf
trace associated with leaf gap
 Often large and divided
A fern
Phylum Psilotophyta – The Whisk
Ferns
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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
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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
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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
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Reproduction
cont’d.:
Phylum Psilotophyta – The Whisk
Ferns
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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
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Collectively called club mosses
• 2 living major genera
− Lycopodium
− Selaginella
• 2 living minor genera
• Several genera became extinct about 270 mya
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Sporophytes have microphylls
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Have true roots and stems
Phylum Lycophyta
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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
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Lycopodium reproduction:
• 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
Phylum Lycophyta
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Lycopodium
reproduction
cont’d.:
Gametophyte
Phylum Lycophyta
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Selaginella - spike mosses
• Abundant in tropics
• Branch more freely than ground pines
• Leaves with ligule on upper surface
Phylum Lycophyta
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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
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Selaginella
reproduction
cont’d.:
Phylum Lycophyta
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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
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Isoetes
reproduction:
• Similar to spike
mosses, except
no strobili
• Sporangia at
bases of leaves
Phylum Lycophyta
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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
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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
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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
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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
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Equisetum
reproduction cont’d.:
Phylum Equisetophyta
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Ancient relatives of horsetails:
• Flourished in Carboniferous, 300
mya
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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
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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
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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
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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 heavywalled, brownish cells =
annulus
Sorus covered by indusium
Phylum Polypodiophyta – The Ferns
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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
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Reproduction
cont’d.:
Phylum Polypodiophyta – The Ferns
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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
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Fossil relatives of ferns cont’d.
• Carboniferous, 320-250
mya - tree ferns abundant
− Seeds found on some of
fossil tree ferns
Phylum Polypodiophyta
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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
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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