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Chapter 23 Seed Plants I: Seed Plants Without Flowers ("…
Chapter 23 Seed Plants I: Seed Plants Without Flowers ("Gymnosperms")
lignophytes
monophyletic group of woody plants
Spermatophytes
seed plants
manoxylic wood
soft parenchymatous wood
pycnoxylic wood
hard strong wood
bidirectionally symmetrical seeds and leaves
has compound leaves with radially symmetrical seeds
Gymnosperms
have naked ovules
angiosperms
flowering plants with sporophylls
Division Progymnospermophyta: Progymnosperms
evolved from trimerophytes
raise later to cycads, conifers
has megaphyllus leaves
produces true woody trees
Orders
Aneurophytales
contain relictial progymnosperms
has vascular cambium and secondary growth
has webbing between ultimate branches
for ex:
Aneurophyton, Proteokalon
Archeopteridales
more derived
8.4 m tall trees with abundant wood
has planted branch system
heterosporous reproduction
For ex:
A. alliana, A.obtusa
Evolution of seeds
has heterospory
megasporium surrounded by integument
has micropyle for sperm to swim
has pollen chamber
Division Pteridospermophyta: Seed Ferns
earlist seed ferms appered in Upper Devonian Period
woody plant with fern like foliage
has a ring of vascular bundle surrounding pith
has large compound, planar leaves
For ex:
Emplectopteris, Schopfiastrum
no double fertilization
Division Coniferophyta: Conifers
moderate gigantic size.
has simple, needle shaped leaves
simple venation
lacks vessels, and sieve tubes
have pollen and seed cones
seed cones are complex
compound cones with shoot and axillary buds
Has two types of shoots
long shoots
short shoots
For ex:
Juniperus, Podocaropus
Division Cycadophyta: Cycads
1-2 m tall
has barks and persistent leaf bases
internally cycads stems resembles the seed ferns.
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produces seed cones and pollen cones.
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For ex:
Cycas revoluta, Zamia florida
Division Cycadeoidophyta: Cycadeoids
has vegetative structure identical to cycads
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individual cones contain both micorsporophylls and megasporophylls
microsporophylls are cup shaped and contain microsporangia
Division Ginkophyta: Maidenhair Tree
only contain one species:
Ginko biloba
unusual
looks like large dicot tree
has broad leaves with dichotomously branched leaves
Ornamental plant
closely related to seed ferns.
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Division Gnetophyta
has three groups of enigmatic plants.
Gnetatum
with 30 species
Ephedra
with 40 species
Welwitschia mirabilis
has vessels in their wood
contain bracts
