Bryophytes213S - Bryophytes - 1 There are about 20,000...

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Bryophytes - 1 There are about 20,000 species of Bryophytes, the plants that lack vascular tissue. They are found throughout the world, although more prevalent in moist and shady areas. Common Bryophyte Habit Bryophytes, especially mosses, are abundant in alpine and artic regions, where they are subjected to freezing. Others are adapted to deserts where they are desiccated most of the time. The moss, Sphagnum , is found in bogs world wide, and forms peat, a source of fuel when compacted, and a soil texturizer when less "decomposed". Lignite, a low-grade coal, contains peat. About 1% of the world’s land mass is comprised of peat bogs. (The United States is about 2% of the world’s land mass.) Associations of Bryophytes with mycorrhizae and with endosymbiotic cyanobacteria that fix nitrogen are common. There are three Bryophyte Phyla: Bryophyta (Mosses) Hepatophyta (Liverworts) Anthocerophyta (Hornworts) The three phyla are distinguished from each other on variations in sporophyte structure and gametophyte morphology. The gametophyte generation is the predominant and assimilative stage in all bryophytes. Major Characteristics of Bryophytes Bryophytes lack vascular tissues so Bryophytes must absorb all water and nutrients at the surface and pass them from cell to cell. This dependence on cell- to-cell diffusion for transport places size restriction on bryophytes. Some mosses have modified water transport cells, call hydroids, that form a central hadrom conducting tissue and a few have solute conducting cells, called leptoids that form a leptom.
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Bryophytes - 2 Some liverworts and hornworts have surface air pores for gas exchange and produce a cuticle. As a group, bryophytes are individually small (2 cm - 20 cm) but often grow in prostrate masses or clumps of upright mosses forming “cushions”. Upright growth without support tissue is not possible. They attach to the substrate with rhizoids that anchor the plant but do not function in absorption. Most bryophytes lack a cuticle layer and grow best in moist, shady habitats, but many can tolerate dry areas by lowering their metabolic needs. (They desiccate.) Bryophyte sperm cells are motile (flagellated) and water, rain or dew, is required for fertilization. Antheridia, the male reproductive structures, are typically apical, and clustered in “cup” to facilitate rain splashes. Archegonia, the female reproductive structures, are also generally apical. The zygote is retained in the archegonium after fertilization and the sporophyte is dependent on the gametophyte for nutrients. Most bryophytes are heterothallic. All are homosporous. Vegetative reproduction by fragmentation and/or gemmae propagules is common.
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Bryophytes213S - Bryophytes - 1 There are about 20,000...

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