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