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Continuing Trends in Plant Evolution

Continuing Trends in Plant Evolution. 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. Seeds. Produced by sporophyte

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Continuing Trends in Plant Evolution

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  1. Continuing Trends in Plant Evolution • 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

  2. Seeds • Produced by sporophyte • Immature seed = ovule (female gametophyte +) • Mature seed functions: • Protection • Embryonic sporophyte • Food source • Also: Pollen grains = reduced male gametophytes

  3. Conifer gametophytes From Ovule to Seed Conifer ovulate scale Conifer pollen grain

  4. Seeds 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 • Germination Conifer seed

  5. Wood • Secondary growth in circumference • Increased support • Reach great heights

  6. Pregymnosperms Early Permean Pangea – dry, continental climates First seed plants

  7. Gymnosperms • 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

  8. Phylum ConiferophytaConifers • 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

  9. Young & old female cones Pinus ponderosa Male cones

  10. ♀ cone scale Sporophyte ♀ ♂ Meiosis Meiosis Pollination Microspores inside microsporangium Gametophytes Megaspores inside megasporangium one functional Seed dispersal & germination Fertilization Fig 30.9

  11. Gymnosperm survey • Conifers • Cycads • Ginkgo • Gnetophytes

  12. Juniper Juniperus Bristlecone Pine Pinus Big Tree, Giant Sequoia Sequoiadendron

  13. H.J. Andrews experimental forest, Blue River Oregon

  14. Douglas fir canopies … to be continued

  15. Maidenhair Tree Ginkgo

  16. Cycads

  17. Welwitschia Mormon Tea Ephedra

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