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Chapter 22: Gymnosperms (Division Cycadophyta: Cycads (compound leaves,…
Chapter 22: Gymnosperms
Division Progymnospermophyta: Progymnosperms
Archaeopteridales
a more derived progymnosperm is Archaeopteris
abundant wood and secondary phloem
Evolution of Seeds
#
earliest progymnosperm is Chauleria
Middle Devonian Period
390 million years ago
Archaeosperma arnoldii
megasporium
integument
micropyle
pollen chamber
holding area
Aneurophytales
relictual progymnosperms
primary xylem
protostele
progymnosperms
third group evolved from trimerophytes
extinct
Division Cycadophyta: Cycads
compound leaves
foliage leaves do not bear ovules
stout trunks
small amount of manoxylic wood
seed cone is large and leaf-like
Division Pteridospermophyta: Seed Ferns
Seed ferns
earliest in Upper Devonian Period
Stenomyelon
three-ribbed protostele
seed fern wood
manoxylic
softer and less dense
conifers and and progymnosperms
tracheids were long and wide
evolved from aneurophytales
leaves similar to true ferns
Division Coniferophyta: Conifers
short roots
simple cones
long shoots
compound cones
#
shoot and axillary bud
cone bracts
short axis bears these
ovuliferous scale
fusing the megasporophylls
Division Ginkgophyta: Maidenhair Tree
short roots = leaves
one living species
dioecious
gymnosperms
cones are not produced
Division Cycadeoidophyta: Cycadeoids
extinct
small distinction from cycads
Division Gnetophyta
three groups of enigmatic plants
Ephedra
40 species
Welwitschia mirabilis
only species in genus
Gnetum
30 species
gymnosperms
vessels in wood
compound
#
small cones
anthophytes
sister clade to flowering plants
