Transcript Vascular Plants
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
system lacked a vascular • 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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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”
bryophytes
Vascular plant phylogeny
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 zygote Diploid egg Haploid gametophyte sporophyte spore
egg
Heterospory
Haploid sperm zygote Diploid sporophyte female gametophyte male gametophyte megaspore microspore
Heterospory evolved many times. Why?
• Increases potential for outcrossing • Specialization of function between micro and 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 + Microphylls Seed plants Megaphylls
Lycopodium
Clubmoss (
Lycopodium
)
Selaginella
Lycophytes
Isoetes Selaginella
Carboniferous lycopods
up to 40 m
Sigillaria Lepidodendron
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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
Spore Spore
Lycopodium
life cycle II Spores dispersed by wind: germinate into a minute gametophyte
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 Tmesipteris
Sporangium 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
(30 spp.) (~60 spp.) and
Ophioglossum Ophioglossum
chromosomes - perhaps more then any other organism can have upwards of 1400
spore bearing sporophore
Ophioglossaceae
Sterile blade
Ophioglossaceae
Botrychium virginianum
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 Sporangia are arranged in sori
Sporangium
Sori
Section through sorus
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 Spores remain viable for a century
Salvinia Marsilea
Osmunda
Osmundaceae
Sporangia loose, not in sori Homosporous
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 • Features of vascular plants • Homospory versus heterospory • Megaphylls vs. microphylls • Life cycle of the fern • Fern allies:
Psilotum
,
Equisetum