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Seed Plants I: Seed Plants Without Flowers ("Gymnosperms")…
Seed Plants I: Seed Plants Without Flowers ("Gymnosperms")
Concepts
lignophytes
monophyletic woody plants
spermatophytes
seed plants
two major suites of characters:
manoxylic wood
very soft
spongy
parenchymatous wood
large compound leaves
radially symmetrical seeds
occurs in cycads and their relatives
pycnoxylic wood
hard
strong wood
little parenchyma
small simple leaves
flattened seeds (biderectionally symmetrical)
occurs in conifers and their relatives
gymnosperms
"naked ovules"
ovules located on flat sporophylls
pine cones
angiosperms
flowering plants
those with carpels
believed to be sporophylls
form tube-like, closed structure
fruits are mature carpels
divisions of seed plants accepted now:
gymnosperms:
2) division Coniferophyta
3) division Ginkgophyta
4) division Gnetophyta
1) division Cycadophyta
angiosperms:
5) division Magnoliopyta
Division Progymnospermophyta: Progymnosperms
third group to evolve from trimerophytes
some gave rise to conifers
cycads
other gymnosperms
developed megaphyllous leaves
evolved vascular cambium
capable of producting:
secondary xylem
secondary phloem
Aneurophytales
relictual progymnosperms (exists as a remnant)
varied in stature
small shrubs
Protopteridium
Tetraxylopteris
large trees (up to 12m)
Aneurophyton
Proteokalon
Triloboxylon
Eospermatopteris
vascular cambium (secondary growth)
primary xylem of stems protostele
Archaeopteridales
more derived progymnosperm
Archaeopteris
trees up to 8.4 m tall
abundant wood
secondary phloem
stems had siphonostele
pith surrounded by primary xylem bundle ring
planated branch systems
"leaflets" spirally arranged simple leaves
heterosporous
megaspores 300 micrometers
microspores 30 micrometers
Evolution of Seeds
megasporangium
microintegument
layer of tissue surrounding megaspore
projects upward
micropyle
hole in the integument
permitted sperm cells to enter
pollen chamber
space at top of megasporangium
became place where microspores settled
microspores evolving into pollen grains
Division Pteridospermophyta: Seed Ferns
cyadophytes
three divisions:
Pteridospermophyta (seed ferns, all extinct)
earliest appeared Upper Devonian Period
form a grade (level of evolution)
any woody plant w/ fern-like foliage that bore seeds
thought to have evolved from Aneurophytales
manoxylic wood (soft/less dense)
Cycadophyta (cycads, extant)
Cycadeoidophyta (cycadeoids, all extinct)
Division Coniferophyta: Conifers
#
diverse (approx. 50 genera and 550 species)
moderate to gigantic size
simple needle or scale leaves
leaves are perennial (persist many years)
one or two veins in center of leaf
has endodermis
transfusion tissue
transfusion parenchyma
transfusion tracheids
pines
monopodial
one main trunk bearing many branches
wood has exclusively tracheids
large-diameter produced in spring
narrow-diameter produced in summer
annual rings
spring wood
summer wood
rays thin and tall
ray parenchyma
ray tracheids
resin canals
produce thick sticky pitch
run vertically among tracheids
horizontally in the rays
phloem
sieve cells
albuminous cells
tall narrow rays
cork cambium
produces thick tough bark
two types of shoot:
long shoot
tiny papery leaves
short shoot
long needle leaves
xeromorphic characters
thick cuticle
sunken stomata
cyclindrical shape
two types of cones:
pollen cones
simple cones
single short unbranched axis
bears microsporophylls
seed cones
more complex
compound cones
shoot
axillary buds
microscopic
cone bracts
short axis leaves
1 more item...
Division Cycadophyta: Cycads
#
most short less than 1 or 2 m tall
trunk covered with bark
persistent leaf bases
stems
similar to seed ferns
thick cortex w/secretory ducts
small amount of manoxylic (parenchymatous) wood
tracheids long and wide
massive rays
reproduction
produce
seed cones
pollen cones
dioecious
each produced on seperate plants
Macrozamia
can reach 18m
Division Cycadeoidophyta: Cycadeoids
all extinct
vegetative features
similar to cyads
differ in subtle details
differentiation of stomatal complexes
leaf trace organization
reproduction
cones containing both
microsporophylls
megasporophylls
Division Ginkgophyta: Maidenhair Tree
single living species
Ginkgo biloba
looks like large dictot
stout trunk
many branches
wood like conifer
lacks vessels
lacks axial parenchyma
broad leaves
dichotomously branched veins
short shoots
long shoots
reproduction
dioecious
gymnospermous
no cones produced
ovules produced in pairs
Division Gnetophyta
3 groups of enigmatic plants:
Gnetum
with 30 species
mostly vines/ small shrubs
broad leaves
Ephedra
with about 40 species
tough shrubs/ bushes
leaves reduced/ scale-like
Welwitschia mirabilis
the only species in genus
short wide stem
only two leaves
grow perennially from basal maristem
continually getting longer
gmnosperms
vessels in wood
evolved from tracheids w/ circular border pits
reproduction
pollen cones
compound
contain small bracts
seed cones
compound
extra tissue layers around ovules
