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Outline. Evolutionary History Alternation of Generations Nonvascular Plants Vascular Plants Seedless Seed Angiosperms Monocots and Eudicots Flowers. Evolutionary History of Plants. More than 98% of all biomass is plants Multicellular photosynthetic eukaryotes 280,000 known species

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  1. Evolution and Diversity of Plants

  2. Outline • Evolutionary History • Alternation of Generations • Nonvascular Plants • Vascular Plants • Seedless • Seed • Angiosperms • Monocots and Eudicots • Flowers

  3. Evolutionary History of Plants • More than 98% of all biomass is plants • Multicellular photosynthetic eukaryotes • 280,000 known species • Thought to have evolved from freshwater algae over 500 mya • Evolution of plants marked by four evolutionary events associated with four major groups of plants • Nonvascular Plants • Advent of nourishment of a multicellular embryo within the body of the female plant

  4. Representatives of theFour Major Groups of Plants

  5. Evolutionary History of Plants • Seedless vascular plants • Advent of vascular tissue • Gymnosperms and angiosperms • Produce seeds • Flowering Plants • Attract pollinators that give rise to fruits

  6. Evolutionary History of Plants

  7. Alternation of Generations • Life cycle involves alternation of generations • Multicellular 1n individuals (gametophytes) produce multicellular 2n individuals (sporophytes) • Multicellular 2n individuals (sporophytes) produce multicellular 1n individuals (gametophytes) • Sporophyte (2n): • Multicellular individual that produces spores by meiosis • Spore is haploid cell that will become the gametophyte • Gametophyte (1n): • Multicellular individual that produces gametes • Gametes fuse in fertilization to form zygote • Zygote is a diploid cell that will become the sporophyte

  8. Alternation of Generations

  9. Alternation of Generations • Appearance of generations varies widely • In ferns, female portions are archegonia and are fertilized by flagellated sperm • In angiosperm, female gametophyte (embryo sac), consists of an ovule • Following fertilization, ovule becomes seed • In seed plants, pollen grains are mature sperm-bearing male gametophytes

  10. Reduction in the Size of the Gametophyte

  11. Other Terrestrial Adaptations • Vascular tissue transports water and nutrients to the body of the plant • Cuticle provides an effective barrier to water loss • Stomata bordered by guard cells that regulate opening, and thus water loss

  12. Protection of Eggs and Embryos

  13. Leaves of Vascular Plants

  14. Nonvascular Plants • Nonvascular plants (bryophytes) • Lack specialized means of transporting water and organic nutrients • Do not have true roots, stems, and leaves • Gametophyte is dominant generation • Produces eggs in archegonia • Produces flagellated sperm in antheridia • Sperm swim to egg in film of water to make zygote

  15. Nonvascular Plants • Hornworts (phlym Anthocerophyta) have small sporophytes that carry on photosynthesis • Liverworts (phylum Hepatophyta) have either flattened thallus or leafy appearance • Mosses (phylum Bryophyta) usually have a leafy shoot, although some are secondarily flattened • Can reproduce asexually by fragmentation • Dependent sporophyte consists of foot, stalk, and sporangium

  16. Hornwort

  17. Liverwort, Marchantia

  18. Moss (Polytrichum) Life Cycle

  19. Vascular Plants • Xylem conducts water and dissolved minerals up from roots • Phloem conducts sucrose and other organic compounds throughout the plant • Lignin strengthens walls of conducting cells in xylem • Most seedless vascular plants are homosporous • Windblown spores are dispersal agents • All seed plants are heterosporous and have male and female gametophytes • Seeds disperse offspring

  20. Cooksonian Fossil

  21. Vascular Tissue

  22. Seedless Vascular Plants • Club Mosses (phylum Lycophyta) • Typically, branching rhizome sends up short aerial stems • Leaves are microphylls (have only one strand of vascular tissue) • Sporangia occur on surfaces of sporophylls • Grouped into club-shaped strobili

  23. Club Moss, Lycopodium

  24. Seedless Vascular Plants • Ferns and Allies • Horsetails (phylum Sphenophyta) • Rhizome produces tall aerial stems • Contains whorls of slender, green branches • Small, scalelike leaves also form whorls at the joints

  25. Horsetail, Equisetum

  26. Ferns • Whisk Ferns (phylum Psilotophyta) • Branched rhizome has rhizoids • Mutualistic mycorrhizal fungus helps gather nutrients • Ferns (phylum Pterophyta) • Large conspicuous fronds • Divided into leaflets • Dominant sporophyte produces windblown spores

  27. Whisk fern, Psilotum

  28. Diversity of ferns

  29. Fern Life Cycle

  30. Seed Plants • Seed plants are the most plentiful plants in the biosphere • Seed coat and stored food allow an embryo to survive harsh conditions during long period of dormancy • Heterosporous • Drought-resistant pollen grains • Ovule develops into seed

  31. Seed Plants

  32. Gymnosperms • Gymnosperms have ovules and seeds exposed on the surface of sporophylls • Confiers • Cycads • Ginkgoes • Gnetophytes

  33. Conifers • Conifers, as well as other gymnosperm phyla, bear cones • Tough, needlelike leaves of pines conserve water with a thick cuticle and recessed stomata • Considered a “soft” wood because it consists primarily of xylem tissue

  34. Pine Life Cycle

  35. Cycads • Cycads (phylum Cycadophyta) • Large, finely divided leaves that grow in clusters at the top of the stem • Pollen and seed cones on separate plants • Pollinated by insects

  36. Cycad Cones Figure 24.19

  37. Ginkgoes • Ginkgoes (phylum Ginkgophyta) • Dioecious • Some trees producing seeds • Others producing pollen • One surviving species (Gingko biloba)

  38. The Ginkgo Tree

  39. Ephedra Figure 24.21

  40. Welwitschia miribilis

  41. Gnetophytes • Gnetophytes (phylum Gnetophyta) • Have similarly structured xylem • None have archegonia • Strobili have similar construction

  42. Angiosperms • Angiosperms (phylum Anthophyta) • An exceptionally large and successful group of plants • Ovules are always enclosed within diploid tissues • Became dominant group of plants in the late Cretaceous and early Paleocene periods

  43. Amborella trichopoda

  44. Monocots and Eudicots • Two classes of flowering plants • Monocotyledones (Monocots) • One cotyledon in seed • Eudicotyledones (Dicots) • Two cotyledons in seed

  45. Flower Diversity

  46. The Flower • Peduncle (flower stalk) expands at tip into a receptacle • Bears sepals, petals, stamens, and carpels, all attached to receptacle in whorls • Calyx (collection of sepals) protect flower bud before it opens • Corolla (collection of petals)

  47. The Flower • Each stamen consists of an anther and a filament (stalk) • Carpel has three major regions • Ovary - Swollen base • Fruit • Style - Elevates stigma • Stigma - Sticky receptor of pollen grains

  48. Generalized Flower

  49. Flowering plant life cycle

  50. Flowers and Diversification • Wind-pollinated flowers are usually not showy • Bird-pollinated flowers are often colorful • Night-blooming flowers attract nocturnal mammals or insects • Usually white or cream-colored • Fruits of flowers protect and aid in dispersal • Utilize wind, gravity, water, and animals for dispersal

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