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Chapter 22: Seed Plants Without Flowers:Gymnosperms (Ginkgophyta:…
Chapter 22: Seed Plants Without Flowers:Gymnosperms
Progymnosperms
Aneurophytales
more relictual progymnosperms
varied in stature
shrubs
large trees
vascular cambium and secondary growth
little webbing between branches but no leaves
primary xylem is proststele like
similar to
rhyniophytes
trimerophytes
examples
Aneurophyton
Proteokalon
Tetraxylopteris
Archaeopteridales
characteristics
large trees
abundant wood
secondary phloem
resemble modern fern leaves
leaflets, spirally arranged simple leaves
reproduction
heterosporous
megaspores/microspores
seeds not produced
stems
siphonostele pith
pith surrounded by xylem bundles
Evolution of Seeds
Earliest known was
Chauleria
integument
surrounds megasporum
layer of tissue projected upward
micropyle
hole that allows sperm to enter
simliar to ovules
pollen chamber
where microspores settle
holding area
gave rise to the carpel in angiosperms
difficult by using fossils
gave rise to conifers, cycads, and other gymnosperms
developed megaphyllous leaves
evolution of a vascular cambium
unlimited growth potential
capable of producing secondary xylem and phloem
Conifers
structure
leaves are needles or scales
simple venation
endodermis or "transfusion tissue"
thick cuticle
sumken stomata
cylindrical shape
cones
pollen cones
simple cones
single, short unbranched axis
bears microsporophylls
gameotophytes shed from tree as pollen
carried by wind, few land in seed cones
seed cones
complex cones
consist of a shoot with axillary buds
short axis bears
cone bracts
ovuliferous scale is formed
most are woody
wood
cork cambian produces bark
monopodial with one main trunk
compsed exclusively of tracheids
annual rings visible
spring and summer wood
Rays contain parenchyma and tracheids
Pollination
sperm
pollen arrives before egg matures
may take over a year for fertilization
pollen tube forms
eggs
two or three archegonia form sets of eggs
loaded in carbs and protein
much largercells
suspensor
zygote doesn't immediate form
first cells to elongate
pushes cells into the megagametophyte
proembryo develops into embryo
no double fertilization occurs
Cyads
external features
stout trunks
compound leaves
internal features
thick cortex
long, wide trachaids
prominent pith
produce seed and pollen cones
diocecious
Occur mostly in tropic regions
Cycadeoids
all extinct
vegetative features nearly identical to cycads
differences of cycads
stomatic complexes
leaf trace organization
individual cones both micro and megasporophylls
Ginkgophyta: Maidenhair Tree
contains single species
Ginkgo biloba
characteristics
stout trunk
many branches
wood like conifers
lacks vessels and exial parenchyma
leaves
broad leaves
dichotomously branched veins
both short and long shoots
ornamental often brillant yellow
Reproduction
dioecious and gymnospermous
ovules occur in pairs and unprotected
cones are not produced
pollen produced in a catkin-like organ
Gnetophyta
Gnetums
mostly vines or small shrubs
leaves similar to dicots
native
east Asia
tropical Africa
Amazon Basin
Ephedra
tough shrubs and bushes
native
northern Mexico
southwestern US
dry mountains of South America
short, wide stem
only two leaves
Pteridospermophyta: Seed Ferns
form a grade rather than clade
based on evolution
not based on common ancestors
thought to have evolved from Aneurophytales
basic features
woody plant
fern-like folaige
bore seeds instead of sori
resembled tree ferns, some were vines
long-lived vascular cambium
produced both xylem and phloem
ring of vascular bundles surrounding pith
woods
basically similar to ancestors
tracheids much longer and wider
several rows of circular bordered pits
rays were many cells wide
manoxylic
softer
less dense than conifers
leaves
large
compound
planar
bore seeds
integument attacted to megasporangioum
