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 features:
- Typically with hollow stems (called culms), plugged at intervals (the nodes).
- Leaves, arising at nodes are alternate, distichous (in one plane) or rarely spiral, and parallel-veined.
- Leaves are 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 are small (called florets), lack petals, and are grouped into spiklets arranged in a panicle, raceme, spike, or head; the flowers are wind-pollinated.
- Fruit is a caryopsis (also called a grain).