Citrus aurantiifolia, key lime (also known as Mexican or West Indian lime), is a thorny shrub or small tree in the Rutaceae (citrus family) that originated in southeast Asia, likely Indonesia and Malaysia, and is cultivated in tropical areas from the West Indies and Central and South America to India, China, and parts of Africa for its flavorful fruit. It is one of several species of Citrus referred to as limes; others include C. hystrix (makrut lime or papeda), C. australasica and C. australis (finger lime and Australian round lime, respectively, both of which are sometimes classified in Microcitrus), and C. glauca (desert lime, sometimes classified in Eremocitrus). C. latifolia, the Persian or Tahitian lime, which is the most widely grown commercial species, can be distinguished from C. aurantiifolia by its larger size, absence of seeds, hardiness, absence of thorns, and longer fruit shelf life.

The most frost-intolerant of the citrus fruits, C. aurantiifolia is a vigorous and drought-resistant shrub or many-branched small tree with numerous sharp spines, 1 cm long (3/8 inch). The leathery, evergreen leaves are alternate, elliptic to oblong, 5 to 7.5 cm (2 to 3 in) long, with narrowly winged stems. The white flowers are solitary or clustered in racemes of 2 to 7; individual flowers are up to 5 cm (2 in) across, with 4 to 6 petals and 20-25 stamens. The small greenish fruits, which ripen to yellow, are generally round to oval or elliptical, around 5 cm (2 in) in diameter, with greenish-yellow, juicy pulp divided into 6 to 15 segments containing few to many small seeds.

C. aurantiifolia was brought to Mediterranean Europe during the Crusades, and then to the Caribbean (likely by the Spaniards) by 1520, where it became locally naturalized throughout the West Indies. It was cultivated in southern Florida and the Florida Keys by the mid-19th century, and became a common “dooryard” fruit, with commercial production in local areas from the 1880s until 1926, when a hurricane destroyed most of the orchards. A public relations campaign to restore the industry, in the 1950s, may have allowed “key lime” to prevail as the common name. This lime is still grown to a limited extent in Florida, but is part of a thriving industry in Dominica, where it is exported to England to be bottled as “Rose’s Lime Juice.”

Key lime, which has a sour, acidic flavor, is sometimes sold as a fresh fruit, but is also widely used for the juice, peels, and the oil obtained from them. Limes are used in sherbet or sorbet, marmalades, jams, and chutneys, and in “Key Lime pie,” although the pie is often made from Persian lime instead. Lime juice is important in sauces and in juice and cocktail beverages, including popular summertime drinks such as daiquiris, mojitos, and Brazilian caiparinhas. Lime juice is low in calories but high in vitamin C. The aromatic leaves are used as a seasoning in Asian cooking. Lime juice is used as a natural remedy to relieve the itch of mosquito bites. In Malaysia and India, the juice is used in traditional medicine to relieve stomach ailments and as an antiseptic, among many other applications.

(Bailey et al. 1976, Morton 1987, van Wyk 2005, Wikipedia 2012.)