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Seed plants I: seed plants without flowers (Division Coniferophyta:…
Seed plants I: seed plants without flowers
Division Progymnospermophyta
Archaeopteridales
Trees upto 8.4 m tall and abundant wood and secondary phloem
Reproduction was heterosporous
More derived Progymnospermophyta
Sporangia were terminal on short branches mixed with sterile, leaf like branch system
Evolution of seeds
Over time, some progymnosperms evolved into seed ferns.
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Microspores were evolving into pollen grains
Earliest known progynosperm is Chauleria, from middle Devonian period
Changes occur in the cell wall, method of germination and the nature of microgametophyte they produced
Aneurophytales
Example-: Aneurophyton, Proteokalon
Varied from shrubs to large trees
Contains the more relictual Progymnosperms
All had vascular cambium and secondary growth
Division Ginkophyta: Maidenhair Tree
Lacks vessels and axial parenchyma
It looks like large dicot tree with stout and trunk and many branches but the wood is like conifers
Contain single living species, Ginkgo biloba
Has broad leave but dichotomously branched veins like seed ferns
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It id dioecious and gymnospermous but cones are not produced
Division Coniferophyta: Conifers
Conifers are never vines, herbs or annuals
They never have bulb or rhizomes, their leaves are needle or scales
They are diverse, 50 genera and 150 species
They posses cones, produce pollen which arrive before egg is mature
Mature embryo has same organization as angiosperm
Seed cones are more complex than pollen cones
Division Cycadeoidophyta: Cycadeoids
Each Microsporophylls was cup shaped and contained numerous microsporangia
Thick fleshy scales found between ovule
Stomatal complexes and leaf trace organization were different in those two groups
All extinct group, had vegetative features almost identical to cycads
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Division Cycadophyta: Cycads
Do not bear ovule, they produce seed cones and pollen cones each on separate plants
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Trunk covered with bark and persistent leaf base
Almost all tropical with unusual distribution
Confused with fern or young palm trees
Believed to have been wide spread and occupies many habitats
Division Pteridospermophyta: Seed ferns
They form a grade rather than a clade
Earliest seed fern appeared in upper Devonian period
Thought to have evolved from Aneurophytales
Classified in 3 division
Had long-lived vascular cambium with xylem and phloem
Leaves of seed ferns were similar to true ferns with branched veins
Division Gnetophyta
Unusual in being gymnosperm with vessels in their wood
Pollen cones and seed cones are compound and contains small bracts
Mostly vines or small shrubs with broad leaves similar to dicots
Pollen is distinctive being spindle shaped and having narrow ridges
Contains 3 groups of enigmatic plants
