Please enable JavaScript.
Coggle requires JavaScript to display documents.
Seed plants without flowers: GYMNOSPERMS, both of these divisions have…
Seed plants without flowers: GYMNOSPERMS
concepts
life cycle of vascular cryptograms is alternate, heteromorphic
the new sporophyte is dependent on the gametophyte as it develops from as a zygote
would be advantageous if the embryo could use the capacities of the leaves and roots of previous sporophyte
to do this the megagametophyte must be retained inside the maternal sporophyte
microgametophytes must change as well because the megagametophyte is positioned in the air instead of near the soil
strobili cannot be reached by swimming sperm cells
the meagasporophyte is cone like and upright allowing it to catch microspores carried by the wind
microgametophyte germinate in the megasporangiate cone producing antheridia dn sperm cells and carry out fertilization
evolution of seeds came after vascular cambium
this could undergo radial growth (girth) and produce trees as massive as redwoods and oaks
we refer to this monophyletic group (derived from one ancestor) as lignophytes
seed plants are called spermatophytes
groups
gymnosperms - naked ovules located on flat sporophylls (like pine cones)
#
angiosperms are the flowering plants that fruit
manoxylic wood contains large amounts of axial parenchyma (cycads)
pycnoxylic wood has little or no axial parenchyma (progymnosperms and gymnosperms)
Division Progymnospermophyta
rhyniophytes gave rise to trimerophytes that gave rise to progymnosperms that gave rise to gymnosperms (conifers, cycads etc)
this group had megaphyllous leaves like ferns and horsetails but unlimited growth potential with the production of secondary vascular tissues
wood was indistinguishable from that of many living conifers
it contained elongate tracheids with circular bordered pits
little or no axial parenchyma
rays were tall and uniserate and had ray tracheids
some species, Triloboxylon and Proteokalon had a cork cambium that produced bark
Progymnosperms are similar to conifers but did not have seeds
aneurophytales
Aneurophyton
Protopteridium
Proteokalon
tetraxylopteris
Triloboxylon
Eospermatopteris
these all had vascular cambium and secondary growth but primary xylem was a protostele
Archaeopteridales
trees with abundant wood and secondary phloem
stems had a siphonostel, pith surrounded by a rind of primary xylem much like modern conifers
the final transition from telomes to leaves occured
sporangia were terminal on short branches, megaspores were released not retained seeds were not produced
Evolution of Seeds
earliest known progymnosperm is chauleria from the middle devonian period, Archaeosperma arnoldii
its megasporangium produced only one megaspore mother cell
megasporangium was covered in a layer of integument
integument - the covering layer over the nucellus of an ovule
micropyle - hole in the integument that permitted the sperm cells to swim to the egg after the megaspore had developed into a megagametophyte and produced egg
pollen chamber - a cavity just above the nucellus in the ovule, the site where pollen accumulates and germinates
Division Pteridospermophyta: seed Ferns
Pteridospermophyta(seed ferns all extinct)
apparently dinosaurs (herbivores) feasted on these seed ferns
leaves similar to ferns in organization but bore seeds
the megasporangium (nucellus) was large with VT bundles running through it, seeds up to 11 cm
swamp forest reconstruction
woody, some are vines
thick cortex around the stem with sclerenchyma
wood is softer and less dense than conifers
a group of extinct vascular plants with seeds but fernlike foliade
Division Cycadophyta: Cycads
confused with either ferns or young palm trees because they have stout trunks with pinnately compound leaves
other than Macrozamia at 18m most cycads are less than 1 or 2 m tall
unlike seed ferns cycad foliage leaves dont bear ovules
they produce seed cones and pollen cones on separate plants
cycads are always dioecious
pollen cones have spiraled shield shaped microsporophylls that bear microsporangia
seed cones vary, 2 or more ovules and are shield shaped as well, vascularized
was a much larger group, now reduced to 10 genera and around 100 species
highly prized ornamentals
found in cuba mexico asia and australia, cannot withstand frost
Division Cycadeoidophyta: Cycadeoids
much like cycads
#
differentiation occurs in stomatal complexes and leaf trace organization as well as cones
the big factor being that cycadeoids contained both microsporophylls and megasporophylls in each cone
Division coniferophyta: Conifers
diverse - 50 genera 550 species, moderate to gigantic size like redwoods of california
they are never vine herbs or annuals and they never have bulbs or rhizomes
conifer leaves are always simple needles or scales
the leaves grow from short shoots and short shoot from long shoots
typical leaes have thick cuticle sunken stomata and cylindrical shape
simple venation one or two long veins running down the center of a needle or scaled shaped leaf
wood
#
lacks vessels, and phloem lacks sieve tubes
tracheids are narrow with one or two rows of bordered pits
pines are monopodial - one trunk bearing many branches
pine wood is composed of tacheids but has annual rings with pring wood and summer wood
spring wood has large diameter tracheids follwed by narrow in the summer
cork cambium produces a thick bark
all conifers have pollen cones and seed cones most of which are woody
Juniperus and podocarpus seed cones are superficially like fruits of flowering plants
pollen cones are simple cones with a single short unbranched axis that bear microsporophylss
pollen is shed and carried by the wind, a small percentage lands in seed cones
seed cones are more complex
they are compound each having a shoot with axillary buds
bears cone bracts rather than sporophylls
in each megasporangium a single large megaspore undergoes meiosis making 4 cells but only one survives as the megaspore
conifer eggs are gigantic cells loaded with carbohydrate and protein
a zygote does not form immediately in a conifer
the first cells elongate as a suspensor and push cells deep into the megagametophyte
these other cells are called the proembryo
Division Ginkgophyta: Maidenhair Tree
one species Ginkgo biloba
unusual stout trunk dicot seeming tree but with wood like conifers
it lacks vessels and axial parenchyma
#
reproductioin is dioecious and gymnospermous but cones are not produced
ovules occur in pairs at the ends of staks
Division Gnetophyta
Gnetum with 30 species
mostly vines or small shrubs with broad leaves similar to dicots
native to asia tropical africa and the amazon basin
ephedra with 40 species
tough shrubs and bushes that are common in the desert regions in northern mexico and southwestern united states and dry mountains in south america
scalelike leaves
Welwithchia mirabilis the only species of its genus
exist in deserts of south africa or are cultivated
short wide stem with two leaves that grow perennially from a basal meristem becoming longer
all three division have vessels in their wood
pollen cones are unlike other gymnosperms being compound
both of these divisions have similar structure yet differ greatly in cones
progymnosperms and conifers had very similar wood
the seed cone is usually a naked ovule waiting for pollen to land in it from the wind
both lack vessels and axial parenchyma
