barley, annual cereal plant ( Hordeum vulgare and sometimes other species) of the family Gramineae (grass family), cultivated by humans probably as early as any cereal. It was known to the ancient Greeks, Romans, Chinese, and Egyptians and was the chief bread material in Europe as late as the 16th cent. It has a wide range of cultivation and matures even at high altitudes, since its growing period is short; however, it cannot withstand hot and humid climates. Today barley is typically a special-purpose grain with many varieties rather than a general market crop. It is a valuable stock feed (often as a corn substitute) and is used for malting when the grain is of high quality. It is a minor source of flour and breakfast foods. Pearl barley is often used in soups. In the Middle East a limited amount of barley is eaten like rice. In the United States most spring barley comes from the western states and most winter barley is grown in the southeastern states for autumn and spring pasture and as a cover crop. Barley is subject to several diseases including smut and rust. Barley is classified in the division Magnoliophyta, class Liliopsida, order Cyperales, family Gramineae.