Lychee

The lychee tree is a slow-growing evergreen that can reach 10 to 15 metres, bearing clusters of fruit with a bumpy red skin. Inside the translucent white aril lies one large, shiny, dark brown seed, oval and about 2 to 3 centimetres long, with a pale scar at one end that gives it a polished chestnut look. The seed is hard, bitter and unpalatable. It is sold in dried slices or granules by Chinese herbal shops under the name lizhi he, and as seeds for planting, although they quickly lose viability once removed from the fruit. The aril itself is sweet, floral and juicy.

Lychee is native to southern China, particularly Guangdong and Fujian provinces, and northern Vietnam, where it has been grown for over two thousand years. It spread to Southeast Asia and India through trade and later to Hawaii, Florida, Madagascar, Mauritius, South Africa and Australia. The English name derives from the Chinese lizhi, which came via Portuguese and other languages into English with spellings such as lichi and leechee. The genus name Litchi is a Latinised form of the same word. The seed has a Chinese name meaning lychee core.

Chinese records mention the lychee from the Han dynasty, when it was considered such a delicacy that the emperor demanded fresh fruit from the south. The most famous story is that of the Tang dynasty concubine Yang Guifei, who adored lychees so much that relay riders were said to carry them over long distances to the capital, a story recorded in poems by Du Mu and others.

In medicine, the seed was recorded in Chinese herbal texts as a remedy for pain in the testes and stomach, and it continues to be used in decoctions, although it is cautioned that the seed is not a food. Cultivation gradually extended from China into Burma and India in the seventeenth century, and into Europe and the Americas in the nineteenth.

A modern chapter concerns safety: outbreaks of acute encephalopathy among undernourished children in northern India and Vietnam were linked to eating large amounts of unripe lychees on empty stomachs. The cause was traced to hypoglycin A and methylenecyclopropylglycine in the fruit, compounds also found in the seed, which interfere with the body's production of glucose. This research raised awareness that the seed and unripe fruit should not be eaten.

Lychee seeds are not used in cooking. In Chinese herbal practice, the dried seed is sliced or powdered and used in decoctions under practitioner guidance for abdominal and pain complaints. The fruit's flesh is eaten fresh, canned, dried (lychee nuts), and used in desserts, drinks, liqueurs, sorbets and cocktails. Fresh seeds are planted to grow new trees, though cultivated varieties are usually propagated by air layering to keep their quality. The wood is dense and was used for carving and for fuel, and the seed's shine makes it popular in craft projects.

The lychee fruit aril provides vitamin C, copper, potassium and polyphenols. The seed, however, is mainly of interest in traditional medicine and laboratory research, where extracts have shown effects on blood sugar and lipid metabolism in animals, but human data are very limited. No dose or use of lychee seed can be recommended as safe or effective on current evidence. Research interest centres on its flavonoids and their possible metabolic activity.