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Chapter 22 (Division Progymnospermophyta (Progymnosperms (evolved from…
Chapter 22
Division Progymnospermophyta
Progymnosperms
evolved from trimerophytes
vascular cambium evolved in progymnosperm
produced large amount of secondary xylem and phloem
wood was similar to conifers , yet had no seed
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reproduction was simple
Aneurophytales
Aneurophyton, Protopteridium., Proteokalon
varied stature from shrubs to large trees
primary xylem of the stem- protostele like the rhyniophytes and trimerophytes
Archaeopteridale
Archaeopteris (Archaeopteridales)
had siphonostele
pith surrounded by a ring primary xylem bundles
similar to conifers and dicots
heterosporous reproduction
megaspores released from sporangia, nor retained
no seed produced
Evolution of Seeds
earliest is Chauleria (390 million yrs ago)
Archaeosperma arnoldii
produced 1 large megaspore mother cell and 3 small abort cells
megasporangium surrounded by layer of integument tissue
micropyle allows sperm cells to swim to the egg
megasporangia evolved into ovules with integument
telomes on near by branches turned into cupules
microspores evolve into pollen grains
middle Devonian Period
Division Pteridospermophyta: Seed Ferns
thought to evolve from Aneurophytales
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were any woody fernlike foliage bore seeds (not sori)
leaves were silimilar of true ferns in overall organization
Division Coniferophyta: Conifers
most diverse
leaves are always simple needles or scales, most are perennial
leaves- simple 1-2 long veins running center
wood lacks sieve tubes
all have pollen and seed cones (woody)
Pines have 2 types of shoot
tiny papery leaves occur on long shoots
axils are short shoots that produce long needle leaves
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pollen cones- single short unbranched axis- bears microsporophylls
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seed cones- compound cones, a shoot with axillary buds
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Division Cycadophyta: Cycads
stem is similar to seed ferns
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thick cortex- secretory ducts surrounds manoxylic wood
leaves do not bear ovules
produce seed and pollen cones (seperate plants)
seed coness variable, most relictual
almost all tropical, unusal distribution
Division of Cycadeoidophyta: Cycadeoids
all extinct
vegetative features almost identical to Cycads
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cones contain microsporophylls & megasporophylls
DIvision Ginkgophyta: Maidenhair
Single living species- Ginkgo biloba
wood is like conifers
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lacks vessels and axial parenchyma
broad leaves- dichotomously branched veins
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not reticulate venation like dicots
reproduction = dioecious and gymnospermous
cones are not produced
female tree produces seeds
Division Gnetophyta3 groups of enigmatic plants
3 groups of enigmatic plants
Ephedra- 40 species
Weleitschia mirabilis- only species in genus
Gnetun- 30 species
unusual in gymnosperms with vessels in wood
gnetophytes are compound contain small bracts
reproduction is interpreted as gnetophytes and flowering plants constitute 2 sister clades- common ancestor
