Chapters 21 & 22

Seedless Vascular and Nonflowering Seed Plants

Topics

• Rhyniophytes

• Evolution of stele – protostele and syphonostele

• Vascular plant cladogram

• Phylum – Lycophyta

• Phylum – Pteridophyta – life cycles

• Adaptive superiority of the seed

• Gymnosperm phyla

Early Vascular Plants: Extinct Rhyniophytes

• Cooksonia spp. - branching sporophyte – homosporous

• Rhynia and Aglaophyton were other Rhyniophytes, early vascular plants similar to Cooksonia

• Today sporangia on vascular plants are lateral – not terminal

Early Vascular Plants• Similarities between the hornworts and vascular plants

make Anthoceros the possible ancestors of vascular plants – inner vascular cylinder = stele

• Protostele (solid – no pith) evolved first – two types

Endarch – central protoxylem Exarch – central metaxylem

Lycophyte roots Lycophyte stems, seed plant roots

cortex

cortexepidermis

epidermis

stele

• Later another type of stele, siphonostele – central pith - stems of ferns and seed plants - will discuss in plant tissues later

Microphylls from enations/scalesMegaphylls from branch systems

Selaginella sp.Lycopodium sp.(ground pine, club moss)

Label – Strobilus axis,sporangium, seta, sporophyll, spores

HOMOSPORY

Phylum - Lycophyta

Label – Strobilus axis,microsporangium, megasporangium, seta, microsporophyll, megasporophyll, microspores, megaspores

HETEROSPORY

Psilotum spp. Whisk ferns

Phylum - Pteridophyta – Ferns and allies

Equisetum spp.Horsetails

Strobilus

Fern stem

Fern root

Ferns - >12,000 spp.

Ferns: Life Cycle

Gymnosperms

• Heterospory - Megasporangium to megaspore to megametophyte to archigonium – all in ovule = egg and other cells = megagametophyle - retained inside the maternal sporophyte

• Fertilized ovule = sporophytic embryo - could use the photosynthetic and absorptive capacity of leaves and roots of mother sporophyte – rather than depending on a tiny haploid gametophyte

Seed ferns are all extinct

Seed – superior propagation

Seed

• Fertilized ovule covered by its integument - seed coat

• Embryonic sporophyte

• Nutritive tissue to nourish sporophyte

• Dormant period

• Not covered by an ovary = Gymnosperms

Gymnosperms <1000 spp.

Four phyla

Phylum - Cycadophyta: Cycads • Only ~100 species today• Almost all tropical • Dioecious – seed cones

and pollen cones on

separate plants

Phylum Coniferophyta = PinophytaMost diverse Gymnosperms - >550 spp.

All moderate to extremely large trees (Sequoia spp. - largest organisms on planet)

Mainly monoecious

Phylum - Ginkgophyta: Maidenhair Tree

• single living species, Ginkgo biloba

• Broad leaves – veins dichotomously branched – not reticulate

• Dioecious – seeds not on cones – emits butric acid – foul odor

• Native to China – medicinal uses

Phylum - Gnetophyta ~ 70 spp.

Gnetum spp. Ephedra spp.

Welwitschia mirabilisOnly sp. in genus

Vessels and sieve tubes

Similarity to Anthophytes

Many – dioecious some - monoecious