Seedless Vascular Plants

Outline

How do seedless vascular plants differ from bryophytes?

Like bryophytes, vascular plants are mostly terrestrial:

• need to avoid desiccation (a beginning at cuticle and stomata)
• need to disperse resistant spores
• need nutrients, light, water, gases

Dominance of the sporophyte

• gametophytes can't get large, because sperm need to swim to eggs
• a bigger sporophyte allows better spore dispersal
• a taller sporophyte is a better competitor for light

Large, terrestrial sporophytes need

• strong support tissue -- lignin
• vascular tissue to conduct nutrients far -- lignin
• specialization into roots, stems, leaves

Early vascular plants

All extinct --420-370 mya

• *Rhyniophyta
• *Zosterophyllophyta
• *Trimerophyta

Charactersitics

reduction of the gametophyte/dominance of sporophyte

organized into tissue systems

• dermal
• vascular
• ground

true vascular tissue

Rhyniophyta

no roots, leaves

vascular tissue

lignified

arranged in a protostele

dichotomously branched with terminal sporangia

Zosterophyllophyta

no roots, leaves

vascular tissue

lignified

arranged in a protostele

sporangia on short lateral branches

gave rise to microphyll line

Trimerophyta

no roots, leaves -- stem with central axis and side branches

vascular tissue

lignified -- better, stronger vacular tissue

arranged in a protostele

sporangia only on some branches

gave rise to megaphyll line

Ferns and "fern allies"

Dominated the "coal age" 380-290 mya, also still living

• Lycophyta -- clubmosses etc.
• Sphenophyta -- horsetails
• Psilotophyta --whisk ferns
• Pterophyta - ferns
• *Progymnospermophyta

Lycophyta -- were dominant trees during the coal age

Lycopodiaceae -- club mosses (Lycopodium)

Morphology

leaves -- microphylls

stems

• protostele
• aerial stems or rhizomes
• strobili w/ sporophylls

roots -- adventitious, from rhizome

Homosporous

Gametophyte often dependent on fungi

Selaginellaceae -- spike mosses (Selaginella)

Similar to club mosses

Heterosporous

Isoetaceae -- quillworts (Isoetes)

Semiaquatic

Heterosporous

Sphenophyta -- horsetails

Extinct genus (Calamites) was a tree

One extant genus: Equisetum

Stem

• hollow: light yet strong
• silica deposits
• rhizome and aerial stem with strobilus

Homosporous -- spores have elators

Psilotophyta

Two genera -- Psilotum and Tmesipteris

Only stem and sporangia -- simplified plant?

Protostele

Homosporous, with heterotrophic gametophyte dependent on fungi

Vocabulary

click here to go to vascular plant vocabulary