grass, any plant of the family Gramineae, an important and widely distributed group of vascular plants, having an extraordinary range of adaptation. Numbering approximately 600 genera and 9,000 species, the grasses form the climax vegetation (see ecology) in great areas of low rainfall throughout the world: the prairies and plains of North America, the savannas and pampas of South America, the steppes and plains of Eurasia, and the veldt of Africa.
Most grasses are annual or perennial herbs with fibrous roots and, often, rhizomes. The stems are always noded and are typically hollow and swollen at the nodes, although many genera have solid stems. The leaves have two parts: a sheath surrounding the stem (called the culm in grasses); and a blade, usually flat and linear. The flowers are of a unique form, the inflorescence being subdivided into spikelets each containing one or more tiny florets. (In other flowering plants the inflorescences are clusters of separate flowers, never spikelets.) The dry seedlike fruit is called a caryopsis, or grain.
Economically the grass family is of far greater importance than any other. The cereal grasses, e.g., wheat, rice, corn, oats, barley, and rye, provide the grain that is the staple food of most of mankind and the major type of feed. The grasses also include most of the hay and pasture plants, e.g., sorghum, timothy, bent grass, bluegrass, orchard grass, and fescue. Popularly the word grass is used chiefly for these latter and for the lawn grass types; it is also loosely applied to plants which are not true grasses (e.g., clover and alfalfa) but which are similarly grown.
Molasses and sugar are products of sugarcane and sorghum, both grasses. Many liquors are made from grains and molasses. Plants of the grass family are also a source of industrial ethyl alcohol, corn starch and byproducts, newsprint and other types of paper, and numerous lesser items. Especially in the tropics, species of reed, bamboo (one of the few woody types), and other genera are used for thatching and construction. As food, grasses are as important for wildlife as for domesticated animals. They are able to survive grazing because their intercalary meristems are set back from the apex of the plant. Because of the tenacious nature of their large underground root system, grasses (e.g., beach grass) are often introduced to prevent erosion. Grasses are classified in the division Magnoliophyta, class Liliopsida, order Cyperales, family Gramineae.
See U.S. Dept. of Agriculture, Grass: The Yearbook of Agriculture (1948); A. S. Hitchcock, A Manual of Grasses of the United States (2 vol., 2d ed. 1971); J. W. Bews, The World's Grasses (1929, repr. 1973).