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Seed Plants w/o Flowers (Division Coniferophyta: Conifers conifer…
Seed Plants w/o Flowers
Division Progymnospermophyta:
Progymnosperms
Evolution of Seeds
Chauleria
Earliest known progymnosperm with heterospory
from Middle Devonian Period
Approx. 390 million years ago
Megasporangium Structure
surrounded by layer of integument
large micropyle
hole in integument
allows sperm to swim to the egg after megaspore develops into megagametophyte and produces eggs
microspores evolved into pollen grains
Pollen chamber
holding area where microspores settled
Aneurophytales
This order contains
Aneurophyton
Protopteridium
Proteokalon
Tetraxylopteris
Triloboxylon
Eospermatopteris
stature varies
shrubs to large trees
up to 12 m tall
Structure
vascular cambium
secondary growth
Primary xylem of stems is protostele
Little webbing bt ultimate branches
Archaeopteridales
more derived progymnosperm
trees up to 8.4 m tall
structure
abundant wood
secondary phloem
stems
siphonostele
pith surrounded by a ring of primary xylem bundles
Heterosporous reproduction
Megaspores up to 300 micrometers in diameter
Microspores up to 30 micrometers in diameter
Structure
megaphyllous leaves
Both secondary xylem and phloem
no seed
no ovule precursors
Gave rise to another line of gymnospermous plants
Cycadophytes
Classified as three divisions
Pteridospermophyta
seed ferns
all extinct
Cycadophyta
cycads
extant
Cycadeoidophyta
cycadeoids
all extinct
Division Pteridospermophyta:
Seed Ferns
Earliest appeared in Upper Devonian Period
Form a
grade
rather than a
clade
level of evolution
all descendants of common ancestor, regardless of their level of evolution
any woody plant with fern-like foliage
bore seeds instead of sori on its leaves
Thought to have evolved from Aneurophytales
both had 3-ribbed protostele
Division Coniferophyta: Conifers
50 genera and 550 species
all conifers
trees of moderate to gigantic size
have pollen cones and seed cones
most are woody
Never
vines
herbs
annuals
have bulbs or rhizomes
Always simple needles or scales
most leaves are perennial
wood lacks vessels
phloem lacks sieve tubes
Pines
two types of shoot
long shoots
tiny papery leaves
short shoots
long needle leaves
xeromorphic characters of leaves
thick cuticle
sunken stomata
cylindrical shape
Pollen cones
simple cones
single short unbranched axis
bears leaves called cone bracts
Seed cones
Compound cones
shoot w/ axillary buds
megasporophylls fuse laterally
forming ovuliferous scale
Division Cycadophyta: Cycads
Frequently confused with
Ferns
Palm trees
Structure
Stout trunk
covered with bark and persistent leaf bases
pinnately compound leaves
short plants
less than 1 or 2 m tall
stems
thick cortex
small amount of manoxylic wood
tracheids are long and wide
rays are massive
support provided by tough leaf bases
produce seed and pollen cones on separate plants
highly prized ornaments
not good with cold weather
Division Cycadeoidophyta:
Cycadeoids
all extinct
features almost identical to cycads
only subtle differences bt the 2
stomatal complexes
leaf trace organization
cones contain both microsporophylls and megasporophylls
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Division Ginkgophyta:
Maidenhair Tree
fossilized remains are found almost everywhere
only species in its division
structure
stout trunk
many branches
wood
like that conifers
lacks vessels and axial parenchyma
leaves
broad
dichotomously branched veins
both short and long shoots
reproduction
dioexious
gymnospermous
no cones produced
ovules
occur in pairs
large
develop 3-layered seed coat
pollen produced in an organ that resembles a catkin
Division Gnetophyta
3 groups of enigmatic plants
Ephedra
40 species
Welwitschia mirabilis
only species
Gnetum
30 species
Gnetum
mostly vines or small shrubs w/ broad leaves
native to
Southeast Asia
Tropical Africa
Amazon Basin
Ephedra
tough shrubs and bushes
common in
desert regions in northern mexico
southwestern United States
dry mountains in South America
leaves reduced and scale like
Welwitschia
few living plants exist in
deserts of South Africa
Cultivation
short, wide stem
only two leaves
grow perennially from basal meristem
too young to know clearly how it evolved
cones
seed
compound and contain extra layers of tissue around ovules
pollen
compound and contain small bracts
Structural
Characteristics
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