The cereal grasses, rice, wheat, maize, barley, oats, sorghum, and millet supply three-fourths of man's energy and over half of his protein. These, with many forage species provide the grain and forage that animals need to produce the meat, milk, and eggs that supplement the cereal diet of humans. Grasses feed the world. They also protect the soil from erosion, cover man's playing fields, and beautify his environment. Grasses and herbivores evolved about the same time.
Grasses are cosmopolitan from the equator to the arctic circle.
Wherever flowering plants will grow, grasses can be found. Grass tribes may be grouped as Panicoid grasses containing the tropical and subtropical species and Festacoid grasses containing the temperate species. The panicoid group contains most of the African grasses. Panicoid grasses do not make use of this advantage under low temperatures and low light intensities. Pearl millet, widely adapted, very drought tolerant and free of prussic acid glucosides, is the best annual summer grazing crop for the southeastern United States.