Rice is a species of grass (family Poaceae) that is an extremely important cereal crop. Two species of rice are grown as food: Oryza sativa and O. glaberrima. The natural range of both these rice species is tropical Asia, although rice can also be cultivated in warm-temperate regions. Of the two species, O. sativa is much more widely grown. In addition, there are seven major varieties of O. sativa (and also a much larger number of minor varieties), variously cultivated on four continents, and each with slightly different characteristics. Rice varieties vary in height from less than 3 ft (1m) to over 15 ft (5 m) tall, and they also vary in other important respects.
Rice is usually cultivated as a semi-aquatic plant that is harvested once a year. Less commonly, there may be several crops per year, or the rice may be cultivated as an upland crop (that is, not in water). Flooded fields used for rice cultivation are sometimes known as "paddies." The portion of the rice plant that is eaten is the seed, called a grain (or caryopsis).
Rice feeds more people in the world than any other crop. The global production of rice was 656 million tons (596 million metric tonnes) in 1999, cultivated over an area of 383 million acres (155 million ha). In the United States, 10.5 million tons (9.6 million tonnes) were grown on 3.6 million acres (1.44 million ha).
Rice has been an extremely important plant in the development of many human cultures, being intimately intermingled in their economy, food resource, and society. For instance, rice plays an important role in Japanese culture. It is viewed as a symbol of health and abundance, is prominent in religious rituals and folklore, and even has deities associated with it. In fact, the emperor of Japan, according to Shinto belief, is the mortal form of the god of the rice plant. Similar cultural aspects showing the importance of rice are seen in societies of India and other Asian nations. In western culture, including the United States, a familiar use for rice that reveals its prominence among grains is its use at weddings—the traditional throwing of rice grains at newlyweds after their matrimonial ceremony is a symbol of fertility, prosperity, and good luck.