POACEAE

also called Gramineae, the grass family of the flowering plant order Cyperales, containing 500 to 650 genera with some 8,000 to 10,000 species. The Poaceae are the most abundant and important family of flowering plants. They grow on all continents, in a wide range of habitats, and they are the world's most important food source. The long, narrow leaves of grasses form sheaths around the stem; the sheaths are usually split and have overlapping edges. The round or flattened stems are often hollow between the joints. The stems may grow upright or be bent at their bases; they may lie on the ground, producing new plants at each joint, or grow just below the surface. Cell division above each joint causes stem elongation. The small flowers lack petals and sepals, are located between two bracts, and are arranged into units called spikelets. The seeds store oil, starch, and protein. The fibrous roots are often greatly branched; when combined with underground or extensive surface stems in perennial species, they prevent erosion. The success of the grasses results in part from their ability to withstand grazing. In most flowering plants, new growth in the aerial plant body occurs at the the shoot tips only, so that the shoot stops growing if the tip is removed. But the growing points, or meristems, of grasses lie at the base of each stem, so that regrowth is possible after removal of the tip by, for example, a grazing animal or a lawnmower. Cereal grasses such as rice, millet, corn (maize), and wheat (qq.v.) are cultivated for the nutritional value of their seeds. Many grass species provide forage for wild and domestic animals; others are used by humans for shelter construction, industrial purposes, erosion control, and ornamentation. Most authorities divide the Poaceae into five or six subfamilies (Pooideae, Panicoideae, Bambusoideae, Chloridoideae, and Arundinoideae; Oryzoideae, a peripheral subgroup of the Bambusoideae, is segregated by some authorities as the sixth subfamily), separated by both anatomic and microscopic characteristics. The subfamilies are further subdivided into tribes. also called Gramineae grass family of monocotyledonous flowering plants, a division of the order Cyperales. The Poaceae are the world's single most important source of food. They rank among the top five families of flowering plants in terms of the number of species, but they are clearly the most abundant and important family of the Earth's flora. They grow on all continents, in desert to freshwater and marine habitats, and at all but the highest elevations. Plant communities dominated by grasses account for about 24 percent of the Earth's vegetation. Additional reading Richard W. Pohl, How to Know the Grasses, 3rd ed. (1978), a nontechnical guide to grass identification; W.D. Clayton and S.A. Renvoize, Genera Graminum: Grasses of the World (1986), exhaustive, up-to-date, and admirably prepared; G.L. Stebbins, Co-evolution of Grasses and Herbivores, Annals of the Missouri Botanical Garden, 68(1):7586 (1981), a relatively nontechnical but thorough discussion of the evolutionary interaction of grasses and grazers; J.M.J. Dewet, Grasses and the Culture History of Man, Annals of the Missouri Botanical Garden, 68(1):87104 (1979), a relatively nontechnical but thorough discussion of the domestication of cereals; Frank W. Gould and Robert B. Shaw, Grass Systematics, 2nd ed. (1983), covering all aspects of the study of grasses, with keys to the grass genera of the United States; James R. Estes, Ronald J. Tyrl, and Jere N. Brunken (eds.), Grasses and Grasslands: Systematics and Ecology (1982), a technical treatment of some aspects of grass evolution, classification, and ecology, covering structural and biochemical diversity, reproductive biology, evolution, systematics of major groups, taxonomic data and analysis, and the past, present, and future of the study of grasses; T.R. Soderstrom and C.E. Calderon, A Commentary on the Bamboos (Poaceae: Bambusoideae), Biotropica, 11(3):161172 (1979), a general account of bamboo biology; F.A. Mcclure, The Bamboos: A Fresh Perspective (1966), a detailed discussion of their growth, reproduction, and classification; Christopher S. Campbell, The Subfamilies and Tribes of Gramineae (Poaceae) in the Southeastern United States, Journal of the Arnold Arboretum, 66(2):123200 (1985), a technical treatment discussing biology, distribution, anatomy, morphology, evolution, and classification; Thomas R. Soderstrom et al. (eds.), Grass Systematics and Evolution (1987), the most thorough treatment of the systematics and evolution of the family; Paul C. Mangelsdorf, Corn: Its Origin, Evolution, and Improvement (1974); Robert W. Jugenheimer, Corn: Improvement, Seed Production, and Uses (1976, reprinted 1985); Frank Blackburn, Sugar-Cane (1984); D.H. Grist, Rice, 6th ed. (1986); D.E. Briggs, Barley (1978).