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Chapter 22: Seed Plants 1 - Coggle Diagram
Chapter 22: Seed Plants 1
Division Progymnospermophyta:
Progymnosperms
Aneurophytales
contains the more widespread progymnopserms
varied from size of shrub to large tree
no actual leaves
Archaeopteridales
Archeopteris
: tall trees w/ abundant wood & secondary phloem
stem had siphonostele pith surrounded by primary xylem bundles
some organisms had complete webbing, considered
megaphylls
reproduction heterosporous, seeds not produced
mega/microspores produced in own distinctive sporangium
megaspores released, not retained, from sporangia
Evolution of Seeds
earliest known heterospory progymnosperm:
Chauleria
from Middle Devonian Period (approx. 390 million yrs ago)
in
Archaeosperma arnoldii
fossil only one megaspore mother cell produced
megasporangium surrounded by
integument
integument has large hole (
micropyle
)
permits sperm cells to swim to egg after megaspore develops into mature megagametophyte
third group to evolve from trimerophytes, now extinct
produces true woody trees
Division Pteridospermophyta:
Seed Ferns
earliest seed ferns appeared in Upper Devonian Period
considered any woody plant w/ fern-like foliage & bore seeds
thought to have evolved from
Aneurophytales
due to earliest seed ferns having 3-ribbed protostele
had long-lives vasc. cambium that produced xylem&phloem
(similar to gymnosperms/angiosperms)
tracheids longer/wider
rays many cells wide&tall
wood was manoxylic
wood was softer/less dense than conifers/progymnosperms
(also occurs in
cycads
&
cycadeoids
leaves similar to true fern, however foliage leaves bore seeds
Division Coniferophyta:
Conifers
approx. 550 species
all trees of moderate to very large size
all have pollen cones & seed cones
pollen cones can be
simple cones
single short unbranched axis w/ microsporophylls
microspore mother cell undergoes meiosis & forms microspores
each develop endosporially into small gametophyte w/ 4 cells
then shed from tree as pollen & carried by wind
seed cones more complex
compound cones
consisting of shoot w/ axillary buds
short axis bears leaves called
cone bracts
, not sporophylls
each bract has axillary bud w/ megasporophylls
modern conifers have microscopic axillary buds
megasporophylls fuse laterally forming
ovuliferous scale
inside megasporangium single megaspore mother cell undergoes meiosis
3 of resulting cells degenerate leaving 1 as megaspore
megasporangium doesn’t dehisce, megaspore retained & grows into large
coenocytic megagametophyte
never vines, herbs, or annuals
never have bulbs/rhizomes
leaves always simple needles or scales
leaves of most are perennial
venation simple
1/2 veins running down center of needle-shaped leaves
several parallel veins in scale-shaped leaves
veins have endodermis & tissue (
transfusion tissue
)
consists of transfusion parenchyma&tracheids
parenchyma cuboidal w/ prominent circular bordered pits
mixed with the tracheids to form complex 3D pattern
facilitates transfer b/t vasc. tissue & mesophyll tissue outside endodermis
wood lacks vessels, phloem lacks sieve tubes
2 types of shoots common
long shoots
w/ tiny papery leaves
short shoots
in axial, produce familiar needle leaf
pollen arrives before egg is mature
more than a year can pass between pollination & fertilization
massive pollen tube slowly digests way to toward megagametophyte as egg forms
zygote does not immediately form embryo
first cells elongate as
suspensor
that pushes other cells deep into megagametophyte
cells pushed deeper develop into embryo (called
proembryo
)
Division Cycadophyta:
Cycads
often confused with ferns/young palm trees due to stout trunks w/ pinnately compound leaves
trunk covered w/ bark & persistent leaf bases
stems similar to seed ferns internally, thick cortex w/
manoxylic
wood
#had manoxylic wood like seed ferns
tracheids long/wide, rays massive
most short, 1-2 meters tall
Macrozamia
can get as tall as 18 meters
foliage leaves do not bear ovules
seed cones & pollen cones produced instead
pollen cones consist of spirally arranged shield-shaped microsporophylls w/ clusters of microsporangia
on separate plants, always
dioecious
about 100 species
thought to be fairly extensive due to range of current species
Division Cycadeoidoohyta:
Cycadeoids
#almost identical vegetative to cycads
all species extinct
had vegetative features almost identical to
cycads
however, individual cones of cycadeoids contain both microsporophylls & megasporophylls
each ovule had stalk, megasporangium surrounded by integument
b/t ovules were thick fleshy scales
microsporophylls located below cluster of megasporophylls
differ only in subtle details in stomatal complexes & leaf trace organization
Division Ginkgophyta:
Maidenhair Tree
#similar wood/shoots to conifer
contains a single living species
Ginkgo biloba
have both
short
and
long
shoots
reproduction dioecious & gymnospermous
looks like large dicot tree w/ stout trunk & many branches
wood similar to conifers
lacks vessels and axial parenchyma
Division Gnetophyta
contains 3 groups of enigmatic plants:
Gnetum
30 species
Ephedra
40 species
tough shrubs/bushes common in desert regions
leaves reduced/scale like
Welwitschia mirabilis
only species
exist only in South Africa or cultivation
have short, wide stem & only 2 leaves
leaves grow perennially from basal meristem, becoming increasingly longer
mostly vines/small shrubs w/ broad leaves (similar to dicots)
unusual due to being gymnosperms w/ vessels in wood
pollen cones
compound
& contain small bracts
seed cones also compact w/ extra layers of tissue around ovules
fossils of organs/tissues too recent to help with evolution of group
possibly shares ancestor with flowering plants
would form “
Division Anthophyta
”
