PLANTS & THEIR EVOLUTION The General Plant Life Cycle: Alternation of Generations Sporophytes are the diploid stage that grow by mitosis from a fertilized egg and produce spores Gametophyes are the haploid stage that develop from by meiosis from spores and produce gametes (egg and sperm) Evolution in General As plants have become more adapted to land the sporophyte generation has become the dominant stage of the life cycle Algae Simple filamentous non-vascular plants adapted to aquatic habitats Moss (P. Bryophytes) 18,600 species Non-vascular gametophyte dominant plants that are adapted (limited) to moist habitats The sporophyte live off the gametophyte and requires water for sperm transport Mosses Life Cycle Fern (P. Pterophyta) >12,000 species Seedless vascular sporophyte dominant plants adapted (limited) to moist habitats Both generations can photosynthesize and water is required for sperm transport Fern Life Cycle Conifers or Cone Bearing Plants (Gymnosperms or P. Coniferophyta) >700 species Sporophyte dominant naked seed bearing (cones) vascular plants adapted to dry and cool habitats (needles) The gametophyte is reduced to a few cells in the spore that produce the sperm or eggs Pollen The male spore/gametophyte is transported in pollen grains Pollen grains are transported by the wind Conifer Life Cycle Flowering Plants (Angiosperms or Anthophyta) >260,000 species Sporophtye dominant seed bearing (flowers) vascular plant adapted to most habitats The gameophyte as in conifers Flowering Plant Life Cycle Flowers & Fruit Many flowering plants have coevolved with pollinators to transfer their pollen Fruits are secondary flower structures that develop to promote seed dispersal