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
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 Root
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 Haploid Diploid sperm zygote egg sporophyte gametophyte spore
Heterospory Haploid Diploid zygote egg sperm sporophyte microspore female gametophyte male gametophyte microspore megaspore
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 + Seed plants Microphylls Megaphylls
Lycophytes Lycopodium Selaginella Clubmoss (Lycopodium) Isoetes
Carboniferous lycopods up to 40 m 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 Thallus Spore 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 Psilotum 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
Equisetum gametophyte (hermaphroditic)
leptosporangiate ferns
Osmunda Most ferns species are Leptosporangiate Ferns Large megaphylls (fronds) unfold lengthwise from a "fiddlehead" Osmunda
Section through sorus Sporangium Sporangia are arranged in sori Sori Indusium Sporangia Sori Section through sorus Sporangia are arranged in sori Sporangium
Fern gametophyte (prothallus)
Ferns Tree ferns (Cyatheaceae) Maidenhair fern 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 Salvinia Marsilea 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
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 Cyathea
Polypodiaceae Asplenium 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