Seedless in Seattle

Occupying the Land  Alternation of generations –Bryophytes – gametophyte dominant  Emphasizes the water requirement for fertilization –Tracheophytes – sporophyte dominant  De-emphasizes the water requirement  Xylem & phloem help meet H 2 0 req.  Lignin strengthens cell walls –Good for H 2 0 transport –Good for erect posture

Occupying the Land  Apical meristems in sporophyte of Tracheophytes allows profuse branching –Bryophytes often have sub-apical growth in sporophyte  Differentiation of plant body of tracheophytes –Roots, stems, leaves  Seeds a key adaptation

Organization of tracheophyte body  Vascular cylinder –Protostele –Siphonostele w/ no leaf gaps –Siphonotele w/ leaf gaps –Eustele w/ leaf trace gaps  Leaves –Microphylls –Macrophylls  Homospory vs. Heterospory –Homosporous – one type of spore produced by meiosis –Heterosporous – two types of spores produced by meiosis

Tracheal elements in “evolutionary” order…

Organization of vascular tissue in “evolutionary” order

Phyla of seedless vascular plants  Rhyniophytes – mid-Silurian to mid- Devonian (425 – 380 mya)  Zosterophyllophyta – Early to late Devonian (408 – 370 mya)  Lycophyta – Devonian to present  Trimerophytophyta – Devonian (395 – 375 mya)  Psilophyta – no fossil record!  Sphenophyta – Devonian to present  Pterophyta – Carboniferous (362 mya) to present

Rhyniophyta  Earliest known vascular plants –Cooksonia  Single, dichotomously branching  Terminal sporangia  Internal stem structure –Epidermis, cortex, phloem-like cells, and water transporting cells intermediate between mosses and ferns  May have had alternation of isomorphic generations  Agalophyton major may be “Prototracheophyte

Agalophyton major

Cooksonia Rhyniophyta

Cooksonia

Rhynia gwynne-vaughanii

Rhynia stem cross-section

Zosterophyllophyta  Also leafless, dichotomously branching  Only upper sections of stems contain stomates  Sporangia borne on lateral stalks  Xylem centripetally differentiated –First to mature at edge of protostele, last to mature in center  Probable ancestor of lycophytes

Zosterophyllophyta Sawdonia

Trimerophytophyta  “Trashcan phylum”  No leaves  Complex branching  Probably much bigger than rhyniophytes or zosters  Xylem differentiated centrifugally – Like Rhyniophytes  Ancestors of ferns & progymnosperms

Trimerophytophyta Pertica

Trimerophytophyta Psilophyton

Lycophyta  Possess microphylls  Protostele in stem & root  Homosporous in some, Heterosporous in others (resurrection fern, quillwort)  Sporophylls – leaves that bear sporangia  May have cones (strobili)  Gametophytes bisexual  Quillworts may not get carbon from atmosphere! –CAM photosynthesis –Secondary growth

Psilophyta  No roots or leaves!  Current molecular evidence leads most botanists to believe these are “degenerate” ferns  Morphology led botanists to believe these were relicts –Still useful in envisioning what ecological role a plant such as Cooksonia might have played  Gametophyte heterotrophic – depends on mycorrhizae

Sphenophyta  Ancient forms were trees – like the Calamites shown below  Whorled microphylls at nodes  Epidermis strengthened with silica – “scouring rush”  Stem complex –Siphonstele –“Vascular bundles” centered on carinal canal  Homosporous –Gametophyte bisexual or male, green

Pterophyta