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Seed Plants I: Seed Plant Without Flowers "Gymnosperms"…
Seed Plants I: Seed Plant Without Flowers "Gymnosperms"
Concepts
ovules located on flat sporophylls example- pine cones
gymnosperms are those plants with naked ovules
Division Progymnospermatophyta
Progymnosperms
Archaeopteridales
more derived progymnosperm was
Archaeopteris
they were up to 8.4 m tall
they had abundant wood & secondary phloem
reproduction was heterosporous
seeds were not produced
Evolution of Seeds
Chauleria
from the Middle Devonian Period
is earliest known progymnosperm species with heterospory
microsporangium was surrounded by layer of integument tissue
there was large micropyle
micropyle is a hole that remitted sperm cells to swim to eggs
pollen chamber where microspores settled
Aneurophytales
contains the more progysperms
they varied in stature from shrubs to large trees up to 12 m tall
they had vascular cambium & secondary growth
they resembled trimerophytes in having litter webbing between branches
Division of Pteridospermophyta
3 divisions
Cycadophyta
cycads, exact
Cyadeoidophyta
cycadeoids all extincts
Pteriospermophyta
seed ferns, all extinct
seed ferns
they had fern like foliage that bore seeds instead of sori
they had long vascular cambium with both xylem & phloem
seed ferns were any woody plant
tracheas were much longer & wide
leaves were similar to of those true ferns
Division Coniferophyta
Conifers
90 m height & 10 m diameter
conifers are never vines, herbs, or annuals neither bulbs or rhizomes
they are diverse: 50 genera & 550 species
leaves
are perennial, resisting for many for many years
simple leaf venation with one or two long veins
pines
tiny papery leaves occur on long shoots
in the axils long needles leaves are short shoots
pollen cones are simple cones with a single short branched axis
compound cones
seed cones are more complex than pollen cones
ovuliferous scale
axillary bud & megasporophylls fused laterally
Division Cycadophyta
Cycads
trunk is covered bark & persistent leaf base
stems are with thick cortex
most are shorts 1or 2 m tall
cycads foliage leaves do not bear ovules
modern cycads are confused with either ferns or young palm trees
produces seed cones & pollen cones on each separate plants
cycads are always dioecious
Division Cycadeiodophyta
Cycadeoids
two groups differential of stomatal complexes & leaf trace organization
cones contained both microsporophylls & megasporophylls
had vegetative features almost identical to cycads
all extinct
Division Ginkgophyta
Maidenhair Tree
looks like large dicot tree with stout trunk & many branches
broad leaves
contains single living species,
Ginkgo biloba
dioecious & gymnospermous but cones are not produced
is beautiful & popular ornamental due to its leaves during autumn
Division Gnetophyta
Ephedra
are tough shrubs & bushes
Gnetum
are mostly vines or small shrubs
Welwitschia
exist only on desert
reproduction is gymnospermous but plant of
Ephedra
&
Gnetum
resemble dicot
contains 3 groups of enigmatic plants
Ephedra
with 40 species
Welwitschia mirabilis
only on genus & species
Gnetum
with 30 species
