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

\