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Seed Plants: Seed Plants Without Flowers (Gymnosperms) (Division…
Seed Plants: Seed Plants Without Flowers (Gymnosperms)
Division Progymnospermophyta
Progymnosperms
Archaeopteridales
more derived from the progymnosperm
trees up to 8.4m tall
abundant wood and secondary phloem
reproduction is heterosporous
seeds were not produced
Evolution of Seeds
integument
layer of tissure surounding the megasporangium
microphyle
hole in the integument that permits sperm cells to swim to the egg
pollen chamber
space at the top of a megasporqangium
a holding area
Aneurophytales
vary in stature
shrubs to large trees
vascualr cambium & secondary growth
but primary xylem was a protostele
resembled trimerophytes
having little webbing between ultimate branches
gives rise later to conifers, cycads, ferns, and horsetails
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Division Pteridospermophyta: Seed Ferns
earliest seed ferns appeared in the Upper Devonian period
any woody plant with fern-like foliage
leaves bore seeds, not sori
leaves were large, compound, and planar
Division Coniferophyta: Conifers
diverse
approx. 550 species
trees moderate to gigantic size
never vines, herbs, or annuals
never have bulbs or rhizomes
their leaves are always simple needles or scales
leaves are perennial, persiting for many years
pines
wood is composed of exclusivley trachiads
2 types of shoot
long shoots
short shoots
both pollen cones and seed cones
Division Cycadophyta: Cycads
short plants, 1 to 2 m
foliage leaves do not bear ovules
produce seed cones and pollen cones on separate plants
highly prizes ornamentals in the warmest parts of the US
almost all tropical
Division Cycadeoidophyta: Cycadeoids
all extinct
had vegetative features similar to cycads
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individual cones contained both microsporophylls and megasporophylls
only differ slightly from cycads in stomatal complexes and leaf trace
Division Ginkgophyta: Maidenhair Tree
contains a single living species
Ginkgo biloba
looks like a large dicot tree
stout trunk and many branches
wood that's like conifers
lacks vessels and axial parenchyma
have both short shoots and long shoots
cones are not produced
popular ornamental tree
males are prefered, females have a bad odor
Division Gnetophyta
contains 3 groups of enigmatic plants
Gnetum
mostly vines or small shrubs
shrubs have broad leaves
the only species of the genus
Ephedra
these plants are tough shrubs and bushes
common in desert regions
leaves are reduced and scale like
Welwitschia mirabilis
few living plants exist only in deserts in South Africa
short wide stem
only 2 leaves
grow perennially from a basal meristem
native to southeast Asia , tropical Africa, and the Amazon Basin
gymnosperms w vessels in their wood
