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 Immature seed = ovule (female gametophyte +) Mature seed functions: *Protection *Embryonic sporophyte *Food source Also: Pollen grains = reduced male gametophytes

From Ovule to Seed Conifer ovulate scaleConifer pollen grain Conifer gametophytes

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

Wood Secondary growth in circumference Increased support Reach great heights

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

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

Phylum Coniferophyta Conifers 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

Young & old female cones Male cones Pinus ponderosa

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

Gymnosperm survey Conifers Cycads Ginkgo Gnetophytes

Big Tree, Giant Sequoia Sequoiadendron Juniper Juniperus Bristlecone Pine Pinus

H.J. Andrews experimental forest, Blue River Oregon

Douglas fir canopies … to be continued

Maidenhair Tree Ginkgo

Cycads

Welwitschia Mormon Tea Ephedra