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Chapter 24 Evolution and Diversity of Plants Outline Evolutionary History Alternation of Generations Nonvascular Plants Vascular Plants Seedless Seed Angiosperms - Monocots and Eudicots - Flowers Evolution and Diversity of Plants 2 Evolution and Diversity of Plants 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 Representatives of the Four Major Groups of Plants 4 Evolution and Diversity of Plants 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 5 Evolutionary History of Plants 6 Alternation of Generations Evolution and Diversity of Plants 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 7 Alternation of Generations 8 Alternation of Generations Evolution and Diversity of Plants 9 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 spermbearing male gametophytes Reduction in the Size of the Gametophyte 10 Evolution and Diversity of Plants 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 Protection of Eggs and Embryos 12 Leaves of Vascular Plants 13 Nonvascular Plants Evolution and Diversity of Plants 14 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 Nonvascular Plants Evolution and Diversity of Plants 15 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 Hornwort 16 Liverwort, Marchantia 17 Moss (Polytrichum) Life Cycle 18 Vascular Plants Evolution and Diversity of Plants 19 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 Cooksonian Fossil 20 Vascular Tissue 21 Seedless Vascular Plants Evolution and Diversity of Plants 22 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 Club Moss, Lycopodium 23 Seedless Vascular Plants Evolution and Diversity of 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 24 Horsetail, Equisetum 25 Ferns Evolution and Diversity of Plants 26 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 Whisk fern, Psilotum 27 Diversity of ferns 28 Fern Life Cycle 29 Seed Plants Evolution and Diversity of 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 30 Seed Plants 31 Gymnosperms Evolution and Diversity of Plants 32 Gymnosperms have ovules and seeds exposed on the surface of sporophylls Confiers Cycads Ginkgoes Gnetophytes Conifers Evolution and Diversity of Plants 33 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 Pine Life Cycle 34 Cycads Evolution and Diversity of Plants 35 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 Cycad Cones Figure 24.19 36 Ginkgoes Evolution and Diversity of Plants Ginkgoes (phylum Ginkgophyta) Dioecious Some trees producing seeds Others producing pollen One surviving species (Gingko biloba) 37 The Ginkgo Tree 38 Ephedra Figure 24.21 39 Welwitschia miribilis 40 Gnetophytes Evolution and Diversity of Plants Gnetophytes (phylum Gnetophyta) Have similarly structured xylem None have archegonia Strobili have similar construction 41 Angiosperms Evolution and Diversity of Plants 42 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 Amborella trichopoda 43 Monocots and Eudicots Two classes of flowering plants Monocotyledones (Monocots) - One cotyledon in seed Eudicotyledones (Dicots) - Two cotyledons in seed Evolution and Diversity of Plants 44 Flower Diversity 45 The Flower Evolution and Diversity of Plants 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) 46 The Flower Evolution and Diversity of Plants 47 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 Generalized Flower 48 Flowering plant life cycle 49 Flowers and Diversification Evolution and Diversity of Plants 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 50 Review Evolutionary History Alternation of Generations Nonvascular Plants Vascular Plants Seedless Seed Angiosperms - Monocots and Eudicots - Flowers Evolution and Diversity of Plants 51 Ending Slide Chapter 24 Evolution and Diversity of Plants