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Chapter 22: Seed Plants w/o Flowers (Coniferophyta: Conifers (Pines (one…
Chapter 22: Seed Plants w/o Flowers
Progymnosperms
gave rise to the conifers, cycads and the other gymnosperms
megaphyllous leaves
evolution of vascular cambium with unlimited growth potential
produces secondary xylem and phloem
Aneurohytales
relitcual progymnosperms
vary from shrubs to trees
all have vascular cambium
have primary xylem with a protostele
secondary growth
Archaeopteridales
all trees with abundant wood and secondary phloem
frond leaves
leaflets spirally arranged simple leaves
heterosporous
Evolution of Seeds
spores are identified as sporophytes
earliest know progymnosperm with heterospory is Chauleria
micropyle
a hole in the integument that permitted the sperm cell to swim after the egg
pollen chamber
where the microspore settled
Pteridospermophyta: Seed Ferns
Pteridospermophyta: Seed Ferns, Cycadophyta: Cycads and Cycadeiophyta: cycadeoids
they form a grade
earliest seed ferns appeared in the Upper Devonian period
any woody plant with fern-like foliage that bore seeds instead of sori
many resembled modern ferns
thought to have evolved from the Aneurophytales
they had the three ribboned protostele
in later evolved species the central cells became parenchyma not tracheids
ring of vascular bundles surrounding pith
wood is manoxylic
much softer and less dense
seeds are extremely large
Coniferophyta: Conifers
very diverse over 550 species
moderate to gigantic size
never herbs, vines or annuals
never have bulbs or rhizomes
leaves are always simple needles or scales
one or two veins running down the center
or have parallel veins in scale-shaped leaves
have an endodermis and tissue called transfusion tissue
perennial , persisting for many years
remain even on very old trunks
lack vessels and their phloem lack sieve tubes
tracheids are narrow with only one or two rows
all have pollen cones and seed cones
most are woody
form extensive forests
Pines
monopodial
one trunk supporting many branches
composed completely of tracheids
rays are thin and tall
Tiny paper leaves have long shoots and their axils are short shoots
pollen cones are simple cones
with a single short unbranched axis
seed cones are more complex
they are compound cones
consist of a shoot and axillary buds
the short axis bear leaves called cone bracts
Cycadophyta: Cycads
contains approximately 100 species
leaves don't bear ovules
produce seed cones and pollen cones
tracheids are long and wide
thick cortex with secretory ducts
trunks are covered in bark and persistent leaf bases
short plants
confused with ferns and young palm trees
short trunks and pinnately leaves
prized ornamentals
almost all tropical
Cycadeoids
vegetative features almost identical to the Cycads
different in stomatal complexes
leaf trace organization
individual cones contain microsporophylls and megasporophylls
each ovule has a stalk
Maidenhair Tree
one single living species
looks like a large dicot tree
stout trunk and many branches
wood like conifers
lacks vessels and axial parenchyma
broad leaves dichotomously branched veins
short shoots that bear leaves and long shoots
reproduction is dioecious and gymnospermous
cones not produced
popular ornamental
