Gymnosperms

  • For the last hundred million years seed plants have been dominant on the landscape
  • Continue the trend of reduction in size of the gametophyte
  • The male gametophyte is pollen which has non motile sperm inside, eliminating the need for water
  • Advantages of seeds
    • Protect and nourish the embryo
    • Can remain dormant for a long time
    • Dispersal through wind, water, and animals
  • Requirements of seed formation
    • Development of an ovule from the sporophyte​
    • Meiosis produces megaspores​ which forms the female gametophyte
    • Egg develops and is fertilized in the gametophyte
    • Embryo produced by zygote​
    • Testa produced by integument of the gametophyte, nourishes the zygote​
  • Gymnosperms have naked or exposed seeds
    • Conifers:
    • Can be shrubs or trees
    • Needle-like or scaley leaves
    • Found in cold and dry environments
    • Seed cones
    • Monoecious
    • Lack vessel elements in their xylem
    • Undergo secondary growth
    • Cycads:
    • Similar in appearance to palm trees
    • Seed cones
    • Flagellated sperm
    • Dioecious
    • Gnetophytes:
    • Xylem has vessel elements
    • Can be trees, shrubs, or vines
    • Seed cones
    • Dioecious
    • Non-flagellated sperm
    • Ginkgos:
    • Only one surviving species
    • Trees
    • Only cultivated
    • Dioecious
    • Cones have a fleshy outer covering