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Seed Plants 1: seed plants without flowers (gymnosperms) (division…
Seed Plants 1: seed plants without flowers (gymnosperms)
Division progymnospermophyta: Progymnosperms
aneurophytales
vary in stature from shrubs to large trees
little webbing between branches
all had vascular cambium and secondary growth
primary xylem of their stems was a protostele
archaeopteridales
more derived progymosperm
trees up to 8.4 m tall
abundant wood and secondary phloem
stems had a siphonostele
pith surrounded by ring of primary xylem bundles
evolution of seeds
earliest known species with heterospory is chauleria
rangier surrounded by a layer of tissue
integument
micropyle
hole in the integument permits sperm cells to swim to egg
pollen chamber
holding area for microspores
division pteridospernophyta:seed ferns
cycadophytes
pteridospermophyta
all extinct
cycadophyta
extant
cyadeoidophyta
all extinct
seed ferns
earliest appeared in upper Devonian period
woody plant with fern like foliage that bore seeds
division coniferophyta: conifers
diverse 550 species
trees are moderate to medium size
never vines herbs or annuals
always simple needles or scales
leaves often simple with one or two veins down center
short shoots
produce long needle leaves
long shoots
tiny papery leaves occur
Division: cycadophyta: cycads
short plants less than 1 or 2m tall
tracheas are long and wide and rays are massive
prominent pith contains secretory canals
larger group
contains nine or ten genera and 100 species
only a few can withstand freezing temperatures
Division cycadeoidophyta: cycadeoids
all extinct
vegetative features
contain both microsporophylls and megasporophylls
Division: ginkgophyta: maidenhair tree
contains single living species
ginkgo biloba
unusual
lacks vessels and axial parenchyma
have short shoots and long shoots
Division Gnetophyta
contains three groups of enigmatic plants
gnetum
30 species
mostly vines or small shrubs
broad leaves
ephedra
40 species
