Biology And The Evolution Of Gymnosperms

PLANTS LECTURE 7
GYMNOSPERMS cont.
Cycadophyta
Ginkgophyta
Gnetophyta—fedrin comes from this plant—pseudophed, this group thought to be closet living relatives of flowering plants BUT not trueat all, they are most closely related to
CONIFEROPHYTA (conifers)—most diverse, very conspicuous at high latitudes and elevations, invulnerable to attacks from microbes and herbivores aka decay andinsect resistant bark and wood contributes to longevity and great size, dominant in harsh environments worldwide
-have thick cuticles on their leaves
-not well respresented in lowland tropics whereangiosperms are most present
INCREASE IN SIZE OF SPOROPHYTE (from bryophytes to gymnosperm) and at the same time REDUCTION OF GAMETOPHYTE GENERATION in seed plants gametophyte become highly reducedand are highly sheltered from the environment
Microspores produced by meiosis to become the male gametophyte in gymnosperms =pollen, grows pollen tube to the egg to make it mature gametophyte(haploid generation) , sometimes pollen has wings (for wind pollination), parastic on the tissues of the ovule as it grows down towards the egg
Female gametophyte is formed form the megaspore that wasgerminated inside the megasporangium, integument protects the contents of the seed and becomes the seed coat, it’s mostly female gametophyte tissue and embedded within is the young 2n sporophyte, thenthe seed dries out, embryo feeds off of the haploid gametophyte tissue
Pollen cones-male, a lot smaller, not woody, have scaled homologous to leaves
Seed cones-female, scales homologous to a branchFleshy cones or seeds of some conifers—often highly reduced, southern hemisphere (junipers to make gin)—animal dispersed vs. wind dispersed
ANGIOSPERMS::major innovations responsible for theirevolutionary success (no dispute that these are a clade! A bit uncertain how they relate to the other seed pants)
Burst 100 mya of them, don’t have fossil intermediary stages of gymnos to angios