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Gymnosperms

Gymnosperms

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Gymnosperms

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  1. Gymnosperms gymno = naked; sperma = seed

  2. Where are we in taxonomy and geological time?

  3. Lifecycle Evolution *** Significant advancements over seedless vascular plants *** • The seed contains an embryonic sporophyte • Protected and surrounded by nutrients for quick germination • Sporophyte grows into a large, usually woody plant • Gametophyte generation is tiny, dependent on the sporophyte and protected/enclosed by it • Female gametophyte remains in the ovule • Male gametophyte is the mature pollen grain • Pollen grain delivers the sperm via the pollen tube • Advantage: this frees gymnosperms from dependency on external water for transporting sperm to the egg • Now they can colonize drier environments!!! Yes!!

  4. Leaves of Gymnosperms • Usually needlelike or leathery • “evergreen” • Coniferous, leaves kept year-round

  5. Phylum Cycadophyta • Unique, ancient plants that are remnants of the lush Carboniferous period: “Age of Dinosaurs” • Often mistaken as palms, if strobili go unnoticed • Examples for research: Cycas and Zamia • Global distribution

  6. Phylum Gnetophyta • This is a small and unique group (only 3 genera) • Ephedra is adapted to desert/grassland habitat • They are evolutionary important, which is thought to be most closely related to Angiosperms • Strobili in a flower-like cluster • Lacks archegonia • Performs double fertilization • Complex xylem vessels

  7. Phylum Ginkgophyta • Unlike most, Ginkgo bilobais a deciduous gymnosperm • Fertilized ovules develop into flesh coated seeds (not fruit?)

  8. Most Gymnosperms are conifers: bearing seeds in cones (strobili) • Phylum Coniferophyta – most numerous and widespread • 50 genera with about 550 living species • Earliest evolution some 300 m.y.a. with drought-resistant features • Tallest vascular plant: “California Redwood Sequoia” • Up to 117m tall and over 11m in trunk diameter • The female gametes: the ovules are NOT in ovaries, but are naked on the surface of cone scales or at the end of branches • Conifers are the most important plants in BC, economically, since most of the forestry industry is based on killing them • The four families (native to N.A.) of conifers found in BC are: • Pinaceae (pine family) • Cupressaceae (cypress family) • Taxodiaceae (bald-cypress family) • Taxaceae (yew family)

  9. Need to know:

  10. Lifecycle highlights • Examples from Pine species (highly representative of all) • 2-year lifecycle from early strobilus to seed development • Microsporangia are borne in Staminate cones (lower region) • Develop from modified leaf called Microsporophyll • Meiosis occurs to produce 4 haploid microspores (pollen grains) • Mitosis occurs to produce a 4-celled pollen grain = male gamete • Shed with wings via wind from the male cone in this condition • When it develops into a mature gametophyte only 2 cells remain • Once inside the female cone, one cell grows into a pollen tube • Fertilization occurs when the sperm nucleus unites with the egg cell • Result is a diploid (2n) zygote, further develops into an embryo within the seed

  11. Lifecycle continues • Megasporangia are borne in “First Spring” Ovulate cones that are red/purple (usually occurs on higher branches) • Develop from a modified branch: seed-scale complex • Meiosis occurs to produce 4 haploid megaspores (one is functional) • Mitosis occurs to produce one mega-gametophyte (multiple eggs) • When non-motile sperm reach the archegonium, fertilization occurs • 6 months are needed to develop a mature seed • Result is a diploid (2n) zygote, further develops into an embryo within the seed coat (2n) but with haploid nutritive tissue

  12. Mature Pine Cones

  13. Juvenile Pine Tree

  14. World’s largest cones?

  15. Grocery Store Botany • Gymnosperm medicinal products: • Ephedra from Gnetophyta • Lots from Pine spp • Gymnosperm edible products: • Dry Gin • Pine Nuts • Ginkgo White Nuts • Gymnosperm resins: • Varnishes • DNA extraction for Jurassic theme parks!

  16. Pine medicines

  17. Flesh surrounding seed? • Yew and Juniper species have a fleshy layer surrounding the seeds, called an Aril (part of mega-gametophyte) • These species lack a normal cone. The flesh is haploid tissue • Not a fruit! But it is considered a “fruiting structure” • What selective advantage does this offer the conifers?

  18. Evolution of 4-16 Nuclei in the Embryo Sac • The difference (is in the female cones) between Gymnosperms and Angiosperm tree-like organisms

  19. Remember to update your Geologic-Botany Time Scale