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

Liverwort spore tetrads - end of Ordovician First fossil of non-algal land plant in Silurian - 430 mya

First flowering plants

Age of Ferns

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

Tree fernTree fern

Sporophyte Sporophyte dominancedominance

Gametphyte

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)

Xylem Phloem QuickTime™ and aTIFF (Uncompressed) decompressor

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Stem

Root

Vascular Bundle

Xylem

• Composed primarily of Tracheids

• Elongated, dead, cells

• Cell wall impregnated with lignin

• Transport of water from soil to leaves

Phloem• Transport via Transport via sieve elementssieve elements

• Elongated, Elongated, living cellsliving cells

• Transport of Transport of sugars, sugars, hormones, etc.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 Tracheophytes that are not seed plants are sometimes seed plants are sometimes called “pteridophytes”called “pteridophytes”

Vascular plant phylogenybryophytes

Cooksonia

lycophytes Ferns + Seed plants

Branched sporophyte

Vascular tissue,Roots

Megaphylls

Microphylls

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

Selaginella (heterosporous)

MegasporangiumMegasporangium

MicrosporangiumMicrosporangium

Lycopodium(homosporous)

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

Haploid

Diploid

Homospory

gametophyte

sperm

eggzygote

sporophyte

spore

HaploidDiploid

Heterospory

femalegametophyte

sperm

eggzygote

sporophyte

megasporemicrospore

malegametophyte

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

Megaphylls

Microphylls

Lycophytes

LycopodiumLycopodium

SelaginellaSelaginella Isoetes

Selaginella

Clubmoss (Lycopodium)

LepidodendronLepidodendronSigillariaSigillaria

Carboniferous lycopodsup to 40 m

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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

Lycopodium life cycle II

Spores dispersed by wind: germinate into a minute gametophyte

Spore Thallus

Rhizoids

Spore

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

Psilotum

Equisetum

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

Sporangium

Reduced forked leaves

Tmesipteris

Psilotum

Psilotum

Psilotum

Dichotomizing stem, no roots Long-lived gametophytes

OphioglossaceaeAdder'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

Ophioglossaceae

Sterile blade

spore bearing sporophore

OphioglossaceaeBotrychium virginianum

Ferns and Fern Allies

Equisetum

EquisetaceaeHorse 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

Calamites (Carboniferous)

Extinct trees

Calamites

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Equisetum gametophyte (hermaphroditic)

leptosporangiate ferns

Osmunda

Most ferns species are Leptosporangiate Ferns

Large megaphylls (fronds) unfold lengthwise from a "fiddlehead"

Section through sorus

Sporangium

Sporangia are arranged in sori

SporangiaIndusium

Sori

Fern gametophyte (prothallus)

Ferns Walking fern

Epiphytic fern (Platycerium)

Maidenhair fern Tree ferns (Cyatheaceae)

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

SalviniaSalvinia MarsileaMarsilea

• 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

Osmundaceae

Sporangia loose, not in soriHomosporous

Osmunda

Leptopteris

Todea

Cyatheaceae

Tree fern growthSporangia in sori on bottom of leafStem usually single and erect

Alsophila

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Cyathea

PolypodiaceaeAsplenium

Adiantum

Pteris

Polypodium

Tectaria

Nephrolepis Elaphoglossum

Main points

• Features of vascular plants• Homospory versus heterospory• Megaphylls vs. microphylls • Life cycle of the fern• Fern allies: Psilotum, Equisetum