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Seed Plants I: Seed Plants without flowers ("gymnosperms") -…
Seed Plants I: Seed Plants without flowers ("gymnosperms")
Division of Progymnospermophyta: Progymnosperms
Aneurophytales
For eg: Aneurophyton, Eospermatoteris, Proteokalon, Ptotopteridium, Tetraxylopteris, Triloboxylon.
Archaeopteridales
For eg: Archaeopteris, Callixylon.
Evolution of seeds
Each sporangium contained only one large megaspore; other three products of the spore mother cell meiosis.
Progymnosperms ate the third group to evolve from trimerophytes.
they give rise to conifers, cycads, and the other gymnosperms.
They produce true woody trees: trunks were up to 1.5m in diameter and 12 m tall.
Division of Pteridospermophyta: Seed Ferns
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Divison Coniferophyta: Conifers
They are diverse 50 genera and 550 species, all trees are gigantic size ex: redwood of California (Sequoiadendron giganteum).
Division of Cycadophyta: Cycads
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Extant
The Cycadophyta are really large, very stiff, the cones can be you a foot tall for the female cones.
Division of Cycadeoidophyta: Cycadeoids
All extinct
Division Ginkgophyta : Maidenhair tree
The ginkgophyta only has one living species, Ginkgo biloba.
Division Gnetophyta
The Gnetophyta are also fairly restricted. There are three genera with approximately seventy-five species. Within the genera, there are three divisions: the gnetum, Ephedra, and welwitschia.
