BIOL 112 Lecture Notes - Lecture 5: Basal Angiosperms, Gnetum, Welwitschia
11 Jan 2017
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10/1/16
Lab 5: Vascular Seed Plants
Gymnosperms: alt. of gens-SPOROPHYTE DOM; heterosporous; 4 extant phyla/taxa
• Coniferophyta (conifers):
o Non-motile sperm carried in pollen grains
o Resinous sap
• Cycadophyta (cycads)
o Dioecious sporophytes
o Pollinated by beetles
o Pollen ruptures and then sperm swims to egg
o transition from water to land adapted reproduction
• Ginkgophyta (ginkgos)
o Dioecious sporophytes
o Stinky females so males usually only used in horticulture
o Pollen ruptures and then sperm swims to egg
o Ovules (female) on branch tips; NO CONES
• Gnetophyta (gnetophytes)
o Gnetum: tropical vines; broad leaves
o Welwitschia: individuals live on dew and fog; taproot supports 2 continuously
growing strap-like leaves
▪ Carry male and female strobili in leaf axils
▪ Namibian desert
o Ephedra: shrubs w/small scale-like leaves and photosynthetic stems; ovules
extrude tube to release sticky fluid traps windblown pollen
▪ Monoecious/dioecious
▪ N.A. deserts
o Synapomorphies w/angiosperms:
▪ Strobili resemble flowers
▪ Similar Xylems
▪ Gnetum and Welwitschia lack archegonia
▪ Pollen tubes transport nonmotile sperm directly to egg
▪ Double fertilization?
Angiosperms:
• Dev. seed protected w/in ovary which matures into fruit
• Flowers and fruits
• Basal angiosperms, magnoliids, eudicots
• Roots, stems, and leaves
• Highly reduced gametophyte; DOM sporophyte
• Pollination→double fertilization:
o One sperm fuses with the egg to form a diploid zygote
o The other sperm nucleus fuses with polar nuclei to form a polyploid endosperm
(3n or 5n)
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