Lychee

Lychee is an evergreen tree 10–20 m tall with a dense, rounded crown, smooth grey-brown bark and durable wood. The leaves are pinnate with 2–8 glossy, lance-shaped leaflets 5–15 cm long that flush coppery-red when young. The small, petal-less, greenish-yellow flowers are borne in branched panicles at the tips of the branches; the tree carries three flower types (male, functionally female and hermaphroditic) that open at different times. The fruit is a spherical to oval drupe 2–3.5 cm long, with a bumpy red to pink rind covered in small polygonal tubercles; inside is a translucent white, juicy, fragrant aril around a single shiny brown seed. It ripens in early summer (May–July in Vietnam) and very quickly; grafted trees bear fruit in 3–5 years.

According to Kew's Plants of the World Online, the native range of Litchi chinensis is southern China (south-western China to Hainan), in the humid subtropics. It has been cultivated in China for more than two thousand years and spread to Vietnam, India, Thailand, Myanmar and the Philippines, and then to Madagascar, Mauritius, South Africa, Brazil, Israel and the Caribbean. The main growing centres today are Guangdong–Guangxi (China), Vietnam, India and Madagascar. In Vietnam the famous lychee areas are Thanh Ha (Hai Duong), Luc Ngan (Bac Giang), Phu Tho and Hung Yen.

The lychee aril is rich in soluble sugars — sucrose, glucose and fructose — giving its deep sweetness and distinctive aroma, and supplies a fairly high level of vitamin C (about 70 mg/100 g fresh fruit). The polyphenol and flavonoid group includes procyanidins, epicatechin and related derivatives; a low-molecular-weight lychee polyphenol extract (oligonol) is produced for food supplements. Unripe fruit and seeds contain two toxins, hypoglycin A and methylenecyclopropylglycine (MCPG), which block glucose production and fatty-acid oxidation and so cause hypoglycaemia. The fruit also provides fibre, potassium and carotenoids.

Lychee is usually eaten fresh, dried (dried lychee), canned or juiced, and its flowers give a fragrant honey. In Chinese and Vietnamese traditional medicine the seeds ('lizhi he'), roots and bark are used for pain and diarrhoea. As for research, the outbreaks of hypoglycaemic encephalopathy in children who ate many unripe lychees in Muzaffarpur (India) have been clarified: Shrivastava et al. (The Lancet Global Health, 2017) established the link between lychee consumption and toxic encephalopathy in malnourished children, with a mechanism involving hypoglycin A and MCPG; epidemiological reports from India (Indian Pediatrics, 2016) and a 2019 review also warn of this risk.

On safety, ripe lychee in moderation is very safe, but eating many unripe fruits, or replacing meals with lychee on an empty stomach — especially in malnourished children — can cause hypoglycaemia, seizures and acute encephalopathy, so young children should not eat lychee as a meal substitute and should not eat unripe fruit. People with diabetes should limit lychee because of its high sugar content. For conservation, the IUCN lists lychee as Least Concern and it is not covered by CITES; it is widely grown in many cultivars, so its genetic resources are maintained mainly through cultivation, but local cultivars and wild genotypes in southern China should be conserved to avoid genetic erosion from the dominance of a few commercial cultivars.