Vascular Plants
Generalized life cycle
Moss life cycle
Spore -> Gametophyte
Gametophyte -> Zygote
Zygote -> mature sporophyte
Sporophyte -> spores
Vascular Plants
Vascular Plants
• Branching sporophyte in
Silurian
• First vascular plants in
Devonian
First flowering plants
Age of Ferns
First fossil of non-algal land plant in Silurian - 430 mya
Liverwort spore tetrads - end of Ordovician
Fossils
• Probable embryophyte
spores at 450 Ma
• Cooksonia fossils in
Silurian (ca. 430 Ma)
Plants like Cooksonia lacked a vascular
system
• Dichotomously-branching
axes
• Terminal sporangia
• No roots or leaves
Over-time became larger, more complex,
and acquired a vascular system
Time
Living vascular plants
(Tracheophytes)
• Stems and roots (often leaves)
Living vascular plants
(Tracheophytes)
• Stems and roots
• Sporophytes dominate the life-cycle
Sporophyte
dominance
Gametphyte
Tree fern
Why sporophyte dominance?
• Spore dispersal by wind: aided by height
• Competition for light (gametophyte
constrained by the need for water)
Living vascular plants
(Tracheophytes)
• Stems and roots
• Sporophytes dominate the life-cycle
• A vascular (transport) system
Vascular system
• Xylem (water transport) and phloem (metabolite
transport)
Stem
Vascular Bundle
Xylem Phloem
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Root
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Xylem
• Composed primarily of
Tracheids
• Elongated, dead, cells
• Cell wall impregnated
with lignin
• Transport of water from
soil to leaves
Phloem
• Transport via sieve
elements
• Elongated, living
cells
• Transport of sugars,
hormones, etc.
3 Major groups of Vascular plants
• Seed plants (gymnosperms
and angiosperms)
• Lycophytes (club mosses
and their relatives)
• Moniliforms (ferns and
fern allies)
Major tracheophyte taxa
• Seed Plants (ca. 290,000 species)
• Lycophytes (ca. 1,100 species)
• Ferns and allies (ca. 11,000 species)
Tracheophytes that are not seed plants
are sometimes called “pteridophytes”
Vascular plant phylogeny
bryophytes
lycophytes
Ferns +
Seed plants
Microphylls
Cooksonia
Megaphylls
Vascular tissue,
Roots
Branched sporophyte
Organ systems origins
• Stems - dichotomous branching
Organ systems origins
• Stems
• Leaves
– Microphylls
Organ systems origins
• Stems
• Leaves
– Microphylls
– Megaphylls
Organ systems origins
• Stems
• Leaves
– Microphylls
– Megaphylls
• Roots
Homospory versus Heterospory
An important variation: Heterospory
Megasporangium
Microsporangium
Lycopodium
(homosporous)
Selaginella (heterosporous)
Heterospory
• Microspores and megaspores produced in
different sporangia on different leaves
(microsporophylls; megasporophylls)
• Microspores grow into male gametophytes
• Megaspores grow into female gametophytes
- remains within spore wall
Homospory
sperm
Diploid
zygote
egg
Haploid
gametophyte
spore
sporophyte
Heterospory
Diploid
egg
Haploid
zygote
sperm
female
gametophyte
male
gametophyte
microspore
megaspore
sporophyte
Heterospory evolved many times.
Why?
• Increases potential for outcrossing
• Specialization of function between microand megagametophyte permits greater
efficiency (less cost)
3 Major groups of Vascular plants
• Seed plants (gymnosperms
and angiosperms)
• Lycophytes (club mosses
and their relatives)
• Moniliforms (ferns and
fern allies)
Moniliforms
Spermatophyta
Lycophyta
Pryer et al. 2001
Lycophytes
•
•
•
•
380 Ma old
1100 spp.
Microphylls only
Sister group to the other living vascular
plants
Lycophytes
• 380 Ma old
• 1100 spp.
• Microphylls only
lycophytes
Ferns +
Seed plants
Microphylls
Megaphylls
LycopodiumClubmoss (Lycopodium)
Lycophytes
Isoetes
Selaginella
Selaginella
Carboniferous lycopods
up to 40 m
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Sigillaria
Lepidodendron
Lycopodium life cycle I
Sporophyte makes
sporangia often in a
“strobilus”
Sporangium
Lycopodium life cycle I
Sporophyte makes
sporangia often in a
“strobilus”
Sporophyll
Sporangium
Lycopodium life cycle II
Spores dispersed by wind: germinate into a
minute gametophyte
Spore
Spore
Thallus
Rhizoids
Lycopodium life cycle III
• Gametophyte produces archegonia and
antheridia (bisexual)
• Biflagellate sperm fertilize egg cells
• New sporophyte grows
Archegonial neck
Lycophyte diversity
• 3 Major groups
– Lycopodiaceae (club mosses)
– Selaginella
– Isoetes
Lycopiaceae
• Approximately 400 species
• Dominated Carboniferous,
up to 40 m tall
– form much of modern coal
• Homosporous
• Archegonia and Antheridia
can take 6-15 years to
mature
Selaginella
• Approximately 700 extant
species
• Heterosporous
• Moist habitats or
"resurrect"
Selaginella umbrosa
Isoetes
• Approximately 200 species
• Grow in water or dried pools
Moniliforms
Spermatophyta
Lycophyta
Ferns and fern allies (moniliforms)
• Includes ferns (Pterophyta) and two small
groups (Psilophyta and Sphenophyta)
• ca. 12,000 spp.
• Homosporous or heterosporous
• Megaphylls (lost in Psilophyta and
Sphenophyta)
• Ecologically important especially as tropical
epiphytes
Moniliforms
Ferns and Fern Allies
Ferns and Fern Allies
Equisetum
Psilotum
Ferns and Fern Allies
eusporangiate ferns
Sporangium wall has 2
or more cell layers
Ferns and Fern Allies
leptosporangiate ferns
Sporangium wall has 1
cell layer
Ferns and Fern Allies
Psilotum and
Ophioglossum
Psilotaceae/Psilophyta
• Psilotum (2 spp.) and Tmesipteris (15 spp.)
• No roots and reduced or absent leaves, photosynthetic
stems
• Sporangia on lateral branches
• Homosporous
• Thought to be "primitive vascular plants", but more likely
simplified due to association with fungi.
Psilotaceae
Psilotum
Sporangium
Tmesipteris
Reduced forked leaves
Psilotum
Psilotum
Dichotomizing stem, no roots
Long-lived gametophytes
Ophioglossaceae
Adder's tongue, eusporangiate ferns
• Homosporous
• Worldwide, common in disturbed areas
• Botrychium (~60 spp.) and Ophioglossum
(30 spp.)
• Ophioglossum can have upwards of 1400
chromosomes - perhaps more then any other
organism
spore bearing sporophore
Ophioglossaceae
Sterile blade
Botrychium virginianum
Ophioglossaceae
Ferns and Fern Allies
Equisetum
Equisetaceae
Horse tails
• Equisetum (15 spp.)
• Homosporous
• Dates back to Devonian, with 20 m high
stems - lots of diversity in Carboniferous
forests
• Extant species "living fossils"
• Leaves whorled, fused into sheaths at base,
only microphylls
Equisetum
Extinct trees
Calamites (Carboniferous)
Calamites
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Equisetum gametophyte (hermaphroditic)
leptosporangiate ferns
Most ferns species are Leptosporangiate Ferns
Large megaphylls (fronds) unfold lengthwise from a "fiddlehead"
Osmunda
Indusium
Sporangia
Sori
Section through sorus
Sporangia are arranged in sori
Sporangium
Fern gametophyte (prothallus)
Maidenhair fern
Tree ferns (Cyatheaceae)
Ferns
Walking fern
Epiphytic fern (Platycerium)
Leptosporangiate ferns
• App. 11,000 species in 25-35 recognized groups
(most of fern diversity)
• Cover 4 of the major clades
- Marsileaceae
- Osmundaceae
- Cyatheaceae
- Polypodiaceae
Marsileaceae
• Mostly aquatic
• Leave blade divided into 2-4 leaflets (clover-like)
• Heterosporous
- megagametophytes with only one archegonium
Symbiotic with cyanobacteria,
fertilized rice fields
Salvinia
Spores remain viable for a century
Marsilea
Osmundaceae
Sporangia loose, not in sori
Homosporous
Osmunda
Todea
Leptopteris
Cyatheaceae
Tree fern growth
Sporangia in sori on bottom of leaf
Stem usually single and erect
Alsophila
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Cyathea
Asplenium
Polypodiaceae
Nephrolepis
Elaphoglossum
Adiantum
Polypodium
Pteris
Tectaria
Main points
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Features of vascular plants
Homospory versus heterospory
Megaphylls vs. microphylls
Life cycle of the fern
Fern allies: Psilotum, Equisetum