Biology, 9th ed, Sylvia Mader Chapter 24 Chapter 24 Evolution and Diversity of Plants Evolution and Diversity of Plants

Outline Evolutionary History Nonvascular Plants Vascular Plants 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 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

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

Evolutionary History of Plants

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

Alternation of Generations

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

Reduction in the Size of the Gametophyte

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

Leaves of Vascular 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

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

Hornwort

Liverwort, Marchantia

Moss (Polytrichum) Life Cycle

Xylem conducts water and dissolved minerals up from roots 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

Cooksonian Fossil

Vascular Tissue

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

Club Moss, Lycopodium

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

Horsetail, Equisetum

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

Diversity of ferns

Fern Life Cycle

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

Seed Plants

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

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

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

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

The Ginkgo Tree

Ephedra Figure 24.21

Welwitschia miribilis

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

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

Amborella trichopoda

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

Flower Diversity

Peduncle (flower stalk) expands at tip into a receptacle 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)

Each stamen consists of an anther and a filament (stalk) 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

Generalized Flower

Flowering plant life cycle

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

Review Evolutionary History Nonvascular Plants Vascular Plants Alternation of Generations Nonvascular Plants Vascular Plants Seedless Seed Angiosperms Monocots and Eudicots Flowers

Biology, 9th ed, Sylvia Mader Chapter 24 Ending Slide Chapter 24 Evolution and Diversity of Plants Evolution and Diversity of Plants