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Chapter 22: Seed Plants Without Flowers "Gymnosperms" (Division…
Chapter 22: Seed Plants Without Flowers "Gymnosperms"
Division of Progymnospermorphyta Progymnosperms
Aneurophytales
relictual progymnosperms
Anerophyton
Protopteridium
Protokalon
Tetraxylopteris
Triloboxylon
Eospermatopteris
varied in stature from shrubs to large trees
all had vascular cambium and secondary growth
primary xylem of stems was protostele like
have little webbing between ultimate branches
not leaves
Archaeopteridales
a more derived progymnosperm
trees up to 8.4m tall
abundant wood and secondary phloem
stems had siphonostele
pith surrounded by ring of primary xylem bundles
webbing partial on some and complete in others
reproduction was heterosporous
megaspores measured up to 300 micrometers diameter
microspores only 30 micrometers in diameter
sporangia
terminal on short branches mixed w/sterile branches
seeds not produced
Evolution of Seeds
spores can be identified w/sporophytes
spores trapped in a sporangium
attached to leaves
attached to wood
spores cannot be identified on gametophytes
except when microscopic and develops w/in spore wall
Chauleria
earliest known progymnosperm w/heterospory
Middle Devonian Period
390 million yrs ago
Archaeosperma arnoldii
megasporangium produced only one megaspore mother cell
one large viable megaspore
three small aborted cells
surrounded by layer of tissue
integument
large micropyle
hole in the integument
permitted the sperm cells to swim
similar to angiosperm ovules
Genomosperma kidstoni
megasporangium was closely surrounded by sterile telomers
G. latens
telomes were fused at base
Eurystoma angulare
similar to Archaeosperma
fused into one structure except at the tip
pollen chamber
microspores were evolving into pollen grains
later gave rise to conifers, cycads, and other gymnosperms
developed megaphyllous leaves
the evolution of a vascular cambium w/unlimited growth potential
produce secondary xylem
produce secondary phloem
wood
elongate tracheids
circular bordered pits
little or no axial parenchyma
rays were tall and uniseriate of procubent ray tracheids
Division Pteridospermophyta: Seed Ferns
Division Coniferophyta: Conifers
diverse
50 gena, 550 species
trees of moderate to gigantic size
giant redwoods of California
reach 90m height, 10 m diameter
never vines, herbs, or annuals
never have bulbs or rhizomes
leaves
are always simple needles or scales
perennial
venation
often simple
1-2 long veins running down center
several parallel veins in scale shaped leaves
veins have an endodermis and tissue
transfusion tissue
transfusion parenchma cells
transfusion tracheids
pollen cones and seed cones
most woody
some resemble fruits of flowering plants
Juniperus
Podocarpus
pines
representative group
modopodial
one main trunk bearing many branches
wood composed exclusively of tracheids
rays are thin and tall and contain both ray parenchyma and tracheids
sticky pith
two types of shoot
long
tiny papery leaves
short needles
pollen cones
simple cones
short unbranched axis
bears microsporophylls
seed cones
compound cones
short axis bears cone bracts
ovuliferous scale
pollen arrives before the egg is mature
pollen tube slowly digests toward megagametophyte as forms
only one zygotes develops into embryo
suspensor
pushes other cells deep into megagametophyte
proembryo
no double fertilization
Division Cycadophyta: Cycads
stout trunks w/ pinnately compound leaves
foliage leaves do not bear ovules
produce seed cones and pollen cones, separate plants
seed cones variable
always dioecious
short plants, less than 1 or 2m tall
trunk covered w/bark and persistent leaf base
remain on plant after lamina and petiole have abscised
stems
thick cortex
contains secretory ducts
tracheids long and wide
rays are massive
always tropical w/unusual distribution
Divsion Cycadeoidophyta: Cycadeoids
all extinct
vegetative features almost identical to those of cycads
differ in the differentiation of stomatal complexes and leaf trace organization
cycadeoids contained both microsporophylls and megasporophylls
each ovule had a stalk
between ovules were thick, fleshy scales
megasporangium surrounded by integument
microsporophylls located below cluster of megasporophylls and cuved upward
megasporophylls
microspor
phyll cup shaped
numerous microsporangia
Divsion Ginkophyta: Maidenhair Tree
wood lacks vessels and axial parenchyma
broad leaves
dichotomously branched veins like seed ferns
not reticulate venation like dicots
short shoots
bear most leaves
long shoots
reproducton
dioecoius and gymnosperms
cones not produced
ovules occur in pairs at the ends of short stalk
unprotected at maturity
pollen produced in organ resembling catkin
stalk
several sporangiophores
two microsporangia
Division Gentophyta
three groups of enigmatic plants
Gnetum
30 species
Welwitschia mirabilis
only species
Ephedra
40 pecies
shrubs and bushes
very common in desert regoins
northern Mexico
SW U.S.A
dry mountains in South America
leaves reduced and scale like
mostly vines or small shrubs w/broad leaves
similar to dicots
native to SE Asia, tropical Africa, Amazon Basin
gymnosperms w/vessels in their wood
vessel elements evolved from tracheids w/ circular bordered pits
pollen cones
compound
contain extra layers of tissue around the ovules
fossils several million tears old
pollen distinctive
spindle shape
narrow ridges
easy to recognize
Triassic period
