Longan

The longan tree is a tall, spreading evergreen with compound leaves and clusters of small round fruit with thin, brittle, tan-brown skins. Peeling reveals a translucent, juicy white aril around a single, round, glossy black seed, about 1 centimetre across, with a pale circular scar that gives the appearance of an eye. The aril is sweet and musky. The seed is hard and bitter and is typically discarded. Sellers offer fresh fruit, canned fruit in syrup, and dried longans with the flesh darkened and chewy, known as guiyuan in Chinese medicine, and sometimes longan seed for planting or herbal use.

Longan is native to the forests of southern Asia, with early cultivation in southern China, northern Thailand, Myanmar and Vietnam. It has long been cultivated in Guangdong, Fujian and Guangxi in China. The Chinese name longyan means dragon's eye, a reference to the eye-like seed visible through the pale flesh when the fruit is cracked open. The Thai name lamyai and Vietnamese nhan are widely used, while the Malay name mata kucing means cat's eye. The species name longan is a Latinised form of the Chinese name.

Chinese literature records longan from at least the Han dynasty, and it was sent as tribute to the imperial court from southern provinces. Dried longan flesh was prized as a tonic in traditional medicine and appears in formulas for the heart and spleen, such as Gui Pi Tang, recorded in later periods.

By the Middle Ages longan growing had spread across Southeast Asia, where northern Thailand developed a major industry around Chiang Mai and Lamphun. Chinese emigrants carried it to Hawaii, Florida, Australia and elsewhere in the nineteenth century, though the tree remained less common than the lychee because it prefers slightly cooler winters to trigger flowering.

An important modern feature is the commercial drying and sulphur treatment of fruit for export, along with canned longans in syrup, which are widely used in Asian desserts. The seed has been investigated by scientists as a source of polyphenols, and in some places the seeds are collected as an industrial by-product for extracts. Longan wood is hard and used in carving and fuel, while the honey from its flowers is a regional specialty.

The seed itself is not eaten. In Chinese herbal medicine, longan seed is dried and ground for topical or oral use under professional guidance, with traditional applications for bleeding and skin conditions. The aril is eaten fresh, canned, or dried, and appears in sweet soups (tong sui) with goji and jujube, teas, jellies, ice creams and drinks. Dried longan is steeped in tea or cooked in congee and chicken soup in China. Longan flower honey is a fragrant specialty. Seeds are also sprouted as planting stock, though plants from seed vary in fruit quality.

The longan fruit is a source of vitamin C, potassium and polyphenols, and dried fruit is an energy-dense food. Laboratory studies show that longan seed extracts contain high levels of antioxidant polyphenols such as gallic and ellagic acids, and animal studies suggest possible effects on blood sugar and inflammation. There are no robust human trials to support any treatment use. Traditional use as a calming tonic is not proven by clinical evidence.