The commercial longan (Dimocarpus longan Lour.) is a highly esteemed arilloid fruit species in Asia and belongs to the family of Sapindaceae. It grows and crops satisfactorily in a range of tropical and subtropical countries but is exploited commercially only in Thailand, China, Taiwan Province of China and recently, Vietnam. Other areas which grow longan include Queensland in Australia and Florida and Hawaii in USA. The longan resembles the lychee (Litchi chinensis) in that the tree is grown for its fleshy, translucent, white aril which surrounds a red brown to black seed from which it separates easily. Fruit can be eaten fresh, frozen, canned or dried. In many countries where both the fruit species are grown, longan has not achieved the importance of the lychee. However, in Thailand longan production is regarded to be more economically important than lychee. Despite this importance there is a general lack of published material on the statistics and production of longan.
Under the family Sapindaceae, the genus Dimocarpus is reported to contain six species of trees and shrubs (Leenhouts, 1971, 1973). Five of the species (Dimocarpus longan, Dimocarpus dentatus, Dimocarpus gardneri, Dimocarpus foveolatus, and Dimocarpus fumatus) are found in Asia from Sri Lanka and India to eastern Malaysia; one (Dimocarpus australianus) exists in Queensland, Australia. Among these species, the most commonly cultivated species is Dimocarpus longan where the taxon Dimocarpus longan spp. longan var. longan is commonly known as the commercial longan. The word 'longan' or 'long yan' or 'lungngan' comes from the Chinese and literally means 'dragon-eye' which is an apt description of the fruit after the skin has been removed. Other vernacular names for longan include 'lam-yai' (Thailand), 'leng-keng' (Malaysia and Indonesia), 'kyet mouk' (Myanmar), 'mien' (Cambodia), 'lam nhai', 'nam nhai' (Laos), and 'nhan' (Vietnam).
Many other scientific names have been given to the longan. These include Nephelium longana (Lam.) Cam. and Euphoria longana Lam. Beside lychee, other related fruits under the Sapindaceae family include the 'rambutan' (Nephelium lappaceum) and 'pulasan' (Nephelium mutabile).