Citrus any of a group of evergreen shrubs and small trees native to tropical and subtropical Asia. The fruits are relatively large, fleshy, and juicy and contain considerable amounts of citric acid and vitamin C. Besides the familiar oranges, lemons, limes, grapefruits, and tangerines, there are many other citruses, including citrons, shaddocks, and bergamots.
Most citruses have thorny branches with long glossy leaves and bear many fragrant white or purple-white blossoms. They crossbreed easily, and many new varieties have been developed in attempts to establish strains that are resistant to cold or produce new kinds of fruits. Among the more than 900 varieties that exist are tangors, crosses between oranges and tangerines; tangelos, crosses between tangerines and grapefruits; and orangelos, crosses between oranges and grapefruits.
Citrus fruits rank second only to grapes as an economically important fruit crop. They are cultivated in warm climates wherever fertile, irrigated soil is available. The extensive groves of Florida, California, and Texas have made the United States the world's largest producer of citrus fruits. Other major citrus-growing countries are Brazil, Spain, Italy, and India.
Citrus trees probably were domesticated in southern China or southeastern Asia about 1000 B.C. They were introduced into the Mediterranean area by Arab traders shortly before the start of the Christian era, and Spanish colonists carried them to Florida in 1565 and to California in 1769.
Citrus fruits have since become important agricultural products in Mediterranean countries, the southern United States (such as Florida), Mexico and South America. All citrus fruits contain citric acid, which has a sour taste like lemon juice. But in many citrus fruits, the sour taste of the acid is overcome by the sweetness of sugar in the fruit. Citrus fruits also contain ascorbic acid (vitamin C) and are important health-giving foods. Flavoring oils can be made from the rinds.
Oranges, lemons and grapefruits are the best-known citrus fruits. They are eaten raw, and used for making flavorings and marmalades.
Mandarins and tangerines are small, orange-like fruits. Unlike oranges, they have a fragrant odor. Limes look like green lemons, and are grown for their juice rather than the fruit itself. On long voyages, sailing ships carried limes to prevent the crew getting scurvy, a condition caused by lack of vitamin C. Kumquats are very sweet fruits resembling small oranges. They may be eaten fresh or candied. Citrons are large sour fruits grown for their rinds, which are used to make oils for perfumes and flavorings. Bergamots are orange-like fruits also used to make perfumes.
Citruses are classified as the genus Citrus of the family Rutaceae (rue). The kumquat, a closely related tree formerly considered a citrus, is now classified in the genus Fortunella.