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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