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Seed plants: seed plants without flowers (Division Cycadophyta: Cycads…
Seed plants: seed plants without flowers
Division Progymnospermophyta: Progymnosperms
Aneurophytales
contains more relictual progymnosperms
Ameirpphyton, Protopteridium, proteokalon, tetraxylopteris, triloboxylon, and eospermatopteris
varied from shrubs to large trees
had little webbing between their branches
these were not leaves
Archaeopteridale
up to 8.4 m tall
abundant wood and secondary phloem
reproduction
heterosporous
megaspores measured up to 300 um in diameter
microspores 30 um in diameter
seeds not produced
Evolution of seeds
spores cannot be identified with gametophytes
except when gametophyte is microscopic
earliest known progymnospecies with heterospory is chaulria
390 mya
archaeosperma arnoldii
produced one megaspore cell
produced on large viable megaspore
produced three small, aborted cells
megasporangium surrounded by tissue
this tissue projected upward
called an integument
a micropyle in the integument
hole that permitted the sperm cells to swim to egg
after megaspore developed into a megagametophyte and produced eggs
simultaneously, microspores were evolving into pollen grains
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later gave rise to conifers, cycads, and other gymnosperms
360 mya, vascular cambium evolved in progymnosperms
it was capable of radial elongation
could function indefinitely
produced large amounts of secondary xylem and phloem
the wood was no different from of many living confiers
leaves and wood were quite advanced
reproduction is simple
Division Pteridospermophyta: seed ferns
classified into three divisions
Cycadophyta
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cycads, extant
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Cycadeoidophyta
cycadeoids, all entinct
pteridospermophyta
seed ferns
all extinct
pteridosperms thought to have evolved from aneurophytales
later species had a ring of vascular bundles
early seed ferns appeared in upper devonian period
seed ferns were any woody plant with fern-like foliage
they bore seeds instead of sori
some were modern tree ferns other vines
seed ferns had a long-lived vascular cambium
produced xylem and phloem
similar to gymnosperms and angiosperms
wood was manooxylic
softer and less dense
Division Coniferophyta: Conifers
diverse 50 genera and 550 species
all moderate to large size
never
vines, herbs or annuals
have bulbs or rhizomes
always simple needles or scales
leaf veins have an edodermis and a tissue called transfusion tissue
pines
pines have both pollen cones and seed cones
seed cones are more complex
compound cones with a shoot and axillary buds
in each megasporangium
mother cell undergoes meiosis
auxillary bud is microscopic
its megasporophylls are fused laterally
pollen arrives before the egg is mature
a year may pass between pollination and fertizilation
Division Cycadophyta: Cycads
often confused with ferns or young palm trees
short plants, 1-2 m tall
trunk covered with bark
persistant leaf bases that remain on the plant
trachieds are long and wide
rays are massive
germination
pollen grains produce
a branched pollen tube
a large, multiflagated sperm cells
can hardly survive the freeing temps of winter
almost all tropical
some in cuba and mexico,
some in Australia and southeast asia
Division Cycadeoidophyta: Cycadeoids
all extinct
vegetative features almost identical to those of cycads
differ in
subtle deatials of stomatal complexes
leaf trace organization
cones contained microsporophylls and megasporophylls
each ovule had a stock
between the ovules were thick, fleshy scales
each microsporophyll was cup shaped with multiple microsporangia
Divison Ginkgophyta: Maidenhair tree
single living species, ginkgo bilboba
looks like a large, dicot tree
both short and long shoots
shoots bear most of the leaves
lacks vessels and axial parenchyma
wood is like that of conifers
has broad leaves
have dichotomously branched veins like seed ferns
reproduction
dioecious and gymnospermous
but cones not produced
ovules come in pairs
occur at the ends of short stalks
unprotected at maturity
pollen is produced in an organ
male trees are preferred,
female tree seeds produce a bad smell
Division Gnetophyta
contains three groups of enigmatic plants
gnetum
30 species
mostly vines or small shrubs
broad leaves similar to dicots
ephedra
40 species
touch shrubs and bushes
very common in desert regions of mexico and US
leaves are reduced and scale like
welwitschia miabilis
exist only in deserts of south africa
short wide stem and only two leaves
leaves are
