continuing trends in plant evolution extreme reduction of water-dependent gametophyte vascular...
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Continuing Trends in Plant Continuing Trends in Plant EvolutionEvolution
• Extreme reduction of water-dependent gametophyte
• Vascular tissue – improved more
• Even more efficient roots, stems, leaves
• Seeds – protection/dispersal of young
• Wood – support
Green: all these are in sporophyte
SeedsSeeds• Produced by sporophyte
• Immature seed = ovule (female gametophyte +)
• Mature seed functions:* Protection* Embryonic sporophyte* Food source
• Also: Pollen grains = reduced male gametophytes
From Ovule to Seed
Conifer ovulate scale Conifer pollen grain
Conifer gametophytesConifer gametophytes
Seeds some moreSeeds some more
• Spores not dispersed
• Reduced gametophytes* Female stays on sporophyte
* Male (pollen grain) dispersed
• Embryo stays on parent sporophyte
• Delayed sporophyte development* Dormancy
* Seed dispersal
* GerminationConifer seed
WoodWood
• Secondary growth in circumference
• Increased support
• Reach great heights
First seed plantsFirst seed plants
• Pregymnosperms• Early Permean• Pangea – dry, continental climates
GymnospermsGymnosperms
• Seeds naked* Often born on scales (modified leaves) of cones* No fruit
• Conifers, cycads, ginkgo, gnetophytes• Some still produce motile sperm• Except for conifers, mostly tropical &
subtropical• First gymnosperms developed in late Permean
Phylum ConiferophytaPhylum ConiferophytaConifersConifers
• Dominate our biomes
• Well adapted to cold & dry summers
• Life cycle typical of gymnosperms* Seeds naked – no fruit* Two kinds of cones
• Male produce spores that grow into pollen grains
• Female produce spores that grow into ovules
Young &
oldfemalecones
Male cones
Pinus ponderosa
Sporophyte
Gametophytes
Mei
osis
Meiosis
♀
♂
Fert
iliza
tion
Pollination
Seed
disp
ersa
l
&
germ
inati
on
Megaspores insidemegasporangiumone functional
Microspores insidemicrosporangium
♀ cone scale
Fig 30.9
Gymnosperm surveyGymnosperm survey
• Conifers
• Cycads
• Ginkgo
• Gnetophytes
Big Tree, Giant SequoiaSequoiadendron
JuniperJuniperus
BristleconePinePinus
H.J. Andrews experimental forest, Blue River Oregon
Douglas fir canopies
… to be continued
Maidenhair TreeGinkgo
Cycads
Welwitschia
Mormon TeaEphedra