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Seed Plants I: Seed Plants Without Flowers ("Gymnosperms") -…
Seed Plants I: Seed Plants Without Flowers ("Gymnosperms")
Concepts
Lignophytes
Monophyletic group of woody plants
Spermatophytes
Seed plants
Manoxylic Wood
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Soft, spongy, parenchymatous wood
Pycnoxylic wood
Hard, strong wood with little parenchyma
Gymnosperms
Plants with "naked ovules"
Ovules on flat sporphlls
Pine cones
Angiosperms
Flowering plants with carpels
Carpels are believed to be sporophylls
Division Progymnospermophyta: Progymnosperms
Aneurophytales
Contains relictual progymnosperms
Varies in stature
Shrubs to large trees
Archaeopteridales
Trees up to 8.4M tall with abundant wood and secondary phloem
Evolution of Seeds
Integument
Layer of tissue
Micropyle
A hole in the integument that lets sperm swim to egg
Pollen chamber
Holding area for pollen
Third group to evolve from trimerophytes
Now EXTINCT
Division Coniferophyta: Conifers
Around 50 genera and 550 species
Simple venation
long and short shoots
Produce either papery leaves or needles
Simple cones
pollen cones
single, short unbranched axis
bears microsporophylls
Compound cones
Seed cones
More complex than pollen cones
Have a shoot with axillary buds
Cone bracts
leaves on the short axis
Division Cycadophyta: Cycads
Frequently confused with ferns or young palm trees
Stout trunks
Pinnately compound leaves
Most are short less than 1-2M tall
Stems are internally same as seed ferns
9-10 genera and 100 species
Division Ginkgophyta: Maidenhair Tree
Single living species
Short shoots and long shoots
Cones are not produced
Ovules occur at end of short stalk in pairs
Unprotected at maturity
Division Cycadeoidophyta: Cycadeoids
EXTINCT
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vegetative features almost identical to cycads
Division Gnetophyta
Mostly vines or small shrubs
Similar to dicots
Native to southeast Asia, tropical Africa, and Amazon Basin
Compound pollen cones with small bracts
Compound seed cones
Contain extra layers of tissue around ovules
Division Pteridospermophyta: Seed Ferns
EXTINCT
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Thought to have evolved from aneurophytales
Manoxylic wood
Softer and less dense than other wood
Thick cortex around the stem
Leaves similar to true ferns
