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Four main groups of Land Plants Bryophytes (mosses, etc.) Ferns and relatives Gymnosperms Angiosperms Bryophytes There are three groups of bryophytes Mosses 12,000 species Liverworts 6,500 species Hornworts 100 species Bryophyte diversity Hornworts 100 species Liverworts 6,500 species Mosses 12,000 species Mosses Mosses - 12,000 species Widely distributed, especially in alpine, boreal, temperate, and tropical forests Able to live in very dry or very cold habitats Many can dry out entirely, then rehydrate Famous mosses: Sphagnum Wetland moss - “peat moss” Boggy regions dominated by it known as peat bogs or peatlands Liverworts and hornworts Liverworts are even less conspicuous than mosses. Some have a lobed appearance. They reproduce both sexually and asexually from small bundles of cells known as gemmae. Hornworts have elongated sporophytes that are hornlike in appearance. They are unusual in that each photosynthetic cell contains one large chloroplast rather than many smaller ones. Bryophytes Bryophytes arose at least 400 mya and possess two adaptations that allow them to survive on land. Waxy cuticle reduces water loss Gametes are protected and develop within gametangia. Bryophytes Bryophytesdo not have a vascular system and so cannot grow very large. Theyalso need moisture to reproduce because fertilization depends on sperm being able to swim through water to reach the egg. In bryophytes the gametophyte (haploid n) is the dominant generation and the sporophyte (diploid 2n) is dependent on the gametophyte. Bryophytes Gametophytes only a few cells thick. No true “leaves”. Directly absorb water & minerals. No lignified vascular tissue. Bryophyte gametophyte Close to the ground. Anchored by rhizoids. Long, tubular single cells - not tissues. Bryophyte sporophyte 3) Capsule 3 parts 2) Stalk 1) Basal foot Bryophyte life cycle meiosis sporophyte spores 2n n embryo gametophyte zygote eggs sperm Bryophyte reproduction Spores produced in capsule (sporangium) Spores released to germinate into gametophytes. Bryophyte reproduction Malegametophytes produce sperm and female gametophytes produce eggs. When there is sufficient moisture sperm swim to the egg and fertilize it. Fertilized egg develops into a zygote and ultimately into a sporophyte. Seedless vascular plants: Ferns and fern allies First vascular plants originated about 420 mya. First seed plants came later about 360 mya. Seedless vascular plants dominated the planet during the Carboniferous period (300-350 mya). Seedless vascular plants: Ferns and fern allies Gianttree ferns, horsetails and lycopods were the dominant vegetation of the Carboniferous period. Theirfossilized remains formed extensive coal beds. Theywere ultimately superseded by the seed plants and far fewer survive today. Present day fern allies Lycopods: About 1,000 species. Includes tropical epiphytes and northern hemisphere low growing club mosses. today about 15 species of Horsetails: Equisetum occur in northern hemisphere in damp conditions. Equisetum Lycopod Ferns A very diverse group about 12,000 species most abundant in the tropics, but distributed worldwide. Most are small to moderately large plants, but tree ferns are many meters tall. Boston fern Common ferns Staghorn fern Maidenhair fern Pteris Fern morphology Dominant generation: sporophyte Fern morphology Body consists of three organs: • Underground rhizome (stem) • Adventitious roots • Fronds (leaves) Fern morphology • Underground rhizome (stem) Fern morphology • Adventitious roots Roots that grow from anywhere but the primary root. Like out of stems. Fern morphology “fiddlehead” • Fronds (leaves) Fern life cycle Independent and meiosis dominant sporophyte spores 2n n embryo Free-living gametophyte zygote eggs sperm Fern life cycle Fern life cycle - spores Unit of dispersal = spores • Produced by sporangia • Sporangia clustered in sori (singular = sorus) • Usually small button-like dots on backs of fronds Fern life cycle - sori Fern life cycle - sori Fern morphology Free-living gametophyte • Also called a prothallus Sporophyte • Produces sperm and eggs • Sporophyte starts attached to gametophyte. Gametophyte dies after sporophyte detaches. Spores and seeds Thespores of ferns are tiny and vast numbers are produced. However, their prospects of survival are low. A new evolutionary innovation, the seed, arose in the Carboniferous Period. Seeds and later fruit proved to be enormously successful and seed plants especially angiosperms came to dominate the planet.
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