The true grasses are monocot (Class Liliopsida) plants of the Family Poaceae (formerly Gramineae). There are some 600 genera and perhaps 10,000 species of grasses. This family includes a great many species of considerable ecological and economic importance, such as lawn and forage grasses, bamboo, wheat, rice, rye, corn, and sugarcane. Agricultural grasses grown for food production are called cereals.
Grasses are generally characterized as having the following characteristics:
- Typically hollow stems (called culms), plugged at intervals (the nodes).
- Leaves, arising at nodes, alternate, distichous (in one plane) or rarely spiral, and parallel-veined.
- Leaves differentiated into a lower sheath hugging the stem for a distance and a blade with margin usually entire; a ligule (a membranous appendage or ring of hairs) lies at the junction between sheath and blade.
- Flowers small (called florets), lacking petals, and grouped into spiklets arranged in a panicle, raceme, spike, or head; the flowers wind-pollinated.
- Fruit a caryopsis (also called a grain).
Cereals constitute the major source of calories for humans, and include rice in India and the Far East, maize in Mexico, and wheat and barley in Europe and North America. Staple food grains are often called corn.
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