Grasses

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Grasses, common name for a large family of flowering plants that is economically and ecologically the most important in the world. The grass family contains about 635 genera and 9000 species, making it the fourth largest family after the legume, orchid, and composite families (see Composite Flowers).

IMPORTANCE

All the world’s cereal crops are grasses, and thus the grass family is economically very important. The world’s 5 top crops produce more tonnage than the next 25 combined, and 4 of the top 5 are the cereals rice, wheat, corn, and barley. Human well-being depends on these few grasses, so even small crop failures of any one of them can produce widespread hunger and economic disruption. In addition, the family provides most of the world’s sugar (see Sugarcane). Another member of the family, bamboo, is an important construction material as well as a food source; it also has been used in papermaking. Citronella, used both in perfumery and as an insect repellent, is an oil distilled from the leaves of certain grasses.

Grasses are the primary source of food for domestic and wild grazing animals, which feed on pastures and grasslands and which are fed hay and silage harvested from them. The total land area devoted to these kinds of croplands is greater than the land area for all other kinds of croplands combined.

Another economically significant use of grasses is for the lawns maintained in many parts of the world. Perennial grasses are well adapted for use in lawns because their basal meristems (growing points) are not lost with mowing. Bermuda grass and zoysia are better adapted to the warm conditions of the southern states. Often special grasses are used where particular conditions of soil or exposure make the more common species unsuitable.

OTHER GRASSLIKE PLANTS

Plants of two other groups, the sedges and the rushes, are superficially similar to grasses and are often confused with them. The three groups are easily distinguished, however, by examining their flowers, stems, and leaves. Rushes have flowers with six-part perianths (floral whorls) and from three- to many-seeded fruits, whereas the flowers of sedges and grasses have no perianth and have single-seeded fruits. Sedges usually occur in moist habitats and have solid stems that are triangular and bear three rows of leaves. Grasses usually occur in dry habitats and have round, hollow stems with two rows of leaves.

Scientific classification: Grasses make up the family Poaceae (formerly Gramineae). Citronella is distilled from grasses of the genus Cymbopogon. Kentucky bluegrass is classified as Poa pratensis. Bent grasses are classified in the genus Agrostis. Fescue grasses are classified in the genus Festuca. Bermuda grass is classified as Cynodon dactylon. Zoysia grasses are classified in the genus Zoysia. Buffalo grass is classified as Buchloë dactyloïdes, carpet grass as Axonopus affinis, redtop as Agrostis gigantea, and annual bluegrass as Poa annua.

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