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Gymnosperms Vascular Plants with Seeds • Seed Plants appeared 425 mya • Seed = embryonic sporophyte with layers of nutritive and protective tissue • Develops from an ovule What are the functions of seeds? Gymnosperm Reproduction • All heterosporous • No antheridia (some archegonia) • Sperm may be motile or nonmotile – Sperm do not swim to egg • Sporophyte dominant Pollen Tubes Gymnosperms Reproduction • Lack flowers and fruits − Do have cones • Ovule exposed on a scale – Not enclosed by tissue − “Naked” at pollination − May become less “naked” after pollination Open vs. Enclosed Heterospory Gymnosperm Reproduction Male Strobilus Gymnosperm Phyla Phylum Coniferophyta Phylum Coniferophyta • • • • • • • Conifers (~600 species) Most common in the temperate zone Largest carbon sink Nonmotile sperm Tracheids only 80% paper and wood “softwood” • Leaf structure variable • Do well in cold and dry environments • Thick cuticle and few stomata American arborvitae Cycadophyta • • • • • Slow-growing Sporophytes resemble palm trees Dioecious Motile sperm Common during Mesozoic Female strobilus (seed cone) • Largest sperm • Neurotoxic Gnetophyta • Only gymnosperms with vessel elements • Nonmotile sperm Welwitschia (1 species) Gnetum (35 species) Ephedra (40 species) Welwitschia • Found only in deserts of SW Africa • long tap root • Short stem • Two leaves Gnetum (35 species) • Tropical vines, shrubs, and trees • Broad leafs with berry-like cones • Resemble flowering plants Ephedra (40 species) • Shrubs and vines • Grow in deserts and other dry temperate & tropical regions • Joint firs Ginkgophyta – – – – Only one living species: Gingko biloba Motile sperm Dioecious Exposed seeds, no cones
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