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Chapter 22: Seed Plants I: Seed Plants Without Flowers (Gymnosperms)…
Chapter 22: Seed Plants I: Seed Plants Without Flowers (Gymnosperms)
Division Progymnospermophyta
Evolution of Seeds
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In free-soring species, spores can be identified with sporophytes if some spores were trapped in a sporangium attached to leaves or woody during fertilization
The life cycle of vascular cryptograms is an alteration of independent, heteromorphic generations
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Archaeopteridales
Reproduction was heteroporous
Megaspores were released from the sporangia, not retained
A more derived progymnosperm was Archaeopteris in the order Archaeopteridales
These were trees up to 8.4 m tall with abundant wood and secondary phloem
Aneurophytales
They all had a vascular cambium and secondary growth, but the primary xylem of their stems was protostele like that of rhiniophytes and trimerophytes
Aneurophytes further resembled trimerophytes in having little webbing between their ultimate branches; these could not yet be called leaves
They varied in stature from shrubs to large trees, up to 12 m tall
The order Aneurophytales contains the more relictual progymnosperms such as
Prototeokalon
Tetraxylopteris
Protopteridium
Triloboxylon
Anuerophyton
Eospermatopteris
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Division Pteridospermophyta: Seed Ferns
Thought to have evolved from the aneurophytales because the earliest seed ferns, had a three-ribbed protostele
Seed ferns, such as Emplectopteris, bore seeds along their leaves, not in cones
The earliest seed ferns appeared in the Upper Devonian Period
Seeds could be extremely large, up to 11 cm long and 6 cm in diameter
Leaves of the seed ferns were similar to those of true ferns in overall organization
Division Coniferophyta: Conifers
Narrow-diameter tracheid in the summer
Rays are thin and tall
Contains both ray parenchyma and ray tracheids
Tiny papery leaves occur on long shoots
Leaves are usually perennial
They are diverse and all are trees if moderate to gigantic size
The giant redwoods of California
