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Plants (Kingdom Plantae) • Multicellular eukaryotes • Photoautotrophs • Terrestrial? – Not all plants are terrestrial • Return to water from land • Move to land was a major step Move to Land Required Significant Adaptations • • • • Water uptake and loss Gas exchange Reproduction Support Move to Land • Plants probably evolved from a group of green algae called the charophytes • Are a fringe species exhibiting multicellular traits • Why a fringe species? Features Common to Green Algae and Plants • Chlorophyll a and other accessory pigments (Chl b, b-carotene) • thylakoid membranes stacked into grana Features Common to Green Algae and Plants • Chlorophyll a and other accessory pigments (Chl b, b-carotene) • similar photosynthesizing organelles • cell walls of cellulose • store carbohydrates as starch • alternation of generation Highlights of Plant Evolution • Four major periods • Move onto land (~425 - 475 mya) – prevent desiccation of whole plant – protect reproductive structures – Features seen in mosses (bryophytes) Highlights of Plant Evolution • Evolution of vascular tissue and diversification (~400 mya) – simple diffusion not an option – Mosses - water-conducting tubes – transport and support – larger body size These are features first seen in ferns, horsetail, whisk ferns ****Similar protection of gametes Whisk Fern Horsetail Highlights of Plant Evolution • Evolution of seed (~360 mya) – additional protection from desiccation and predation – dispersal Highlights of Plant Evolution • Emergence of flowering plants (~130 mya) – Seeds in protective ovary – Expanded potential for diversity – Complex structure with great potential for adaptation – Greater sexual reproductive success – Coevolution between insects and angiosperms Nontracheophytes • • • • • • Mosses, liverworts and hornworts Probably closest to ancestral form protected gametangia lack vascular tissue Encrusting Water needed for fertilization Gametophyte Sporophyte Sporophyte relies on gametophyte for nutrients Nonseed Tracheophytes Plants • Ferns, horsetail, club mosses • Retain some traits of mosses • Evolved some traits also seen in seedproducing vascular plants Traits Shared with Nontracheophytes • Antheridia and archegonia retain similar structure • Require water/moisture for sexual reproduction • Production of spores Traits Shared with Seed-Producing Plants • Vascular tissue - greater body size • Sporophyte is dominant stage of life cycle Sporophyte Gametophyte Seedless tracheophytes were the dominant vascular plants for ~ 50 million years • Continents in tropical/subtropical zone • As continents drifted away from equator, conditions changed • Seed-producing plants were present during height of seedless vascular plant success Rise of Seed-Producing Tracheophytes • Well suited for environmental changes • Gametophyte smaller and retained in moist tissues of sporophyte • Pollination rather than swimming sperm • Evolution of seed • gymnosperms and angiosperms Gymnosperm • • • • • • “naked seed” still have a seed coat four divisions Coniferophyta best known evergreens needle-shaped leaves, thick cuticle Sporophyte Gametophyte Gametophyte passes within sporophyte Angiosperms • “protected seed” • most diverse group – 235,000 known species vs. 721 species of gymnosperms • One division - Anthophyta • Two classes – Monocotyledones – Dicotyledones Angiosperms • successful and effective design • different themes of the same design Sporophyte Gametophyte Gametophyte passes within sporophyte Develops into fruit Develop into seeds
