Longan

Overview

The Longan (Dimocarpus longan) is native to southern China in elevation about 150 to 700 m. In India, Sri Lanka, Upper Myanmar, North Thailand, Kampuchea, North Vietnam, and New Guinea, the species has also been present. In Southeast Asia, Australia, and the United States, the crop is primarily grown, and sparse trees are found at higher elevations.

Vernacular Names

Lengkeng (Malaysia), Ash-fol (India), Rongan (Japanese), Lóng yǎn (Chinese), Longan (French), Longane (German), Lengkeng (Dutch).

Agroecology

Longan (Dimocarpus longan) is adapted to warm subtropical regions or to higher elevations in the tropics where temperature variations for adequate flowering are distinct. For prolific flowering, Longan needs a short cool winter season or a short drought in winter can support flowering. High temperatures do not hamper growth from the fruit set onwards, but nights should not be warmer than 20 to 25 °C. Annual rainfall of 1,500 to 2,000 mm is needed for the trees. From the fruit set until maturity, sufficient soil moisture is needed. Longan prefers thick sandy loams that are well-drained.

Morphology

• Trunk - rough corky with a diameter reaching cultivation 1 m and dark-brown, lenticellate twigs. 
• Leaves - alternate, 2–10 cm long. The leaflet is oblong-elliptic to oblong-lanceolate, upper surface glossy deep green, lower pale green. New growth is wine-colored.
• Flowers - Inflorescences terminal or axillary near apex, large, many-branched, 8–40 cm long, densely tufted tomentose. Panicle comprises staminate, pistillate, and hermaphrodite flowers.
• Fruit - drupaceous, 1.25–3 cm in diameter, subglobose, usually yellowish-brown or sometimes grayish-yellow, mostly pusticulate to granulate, and nearly smooth.
• Seed - globular with shining blackish-brown testa and enveloped by a fleshy, translucent, white arilloid.

Cultivation

• Propagation is by seeds and cuttings.
• Depending on the method trees take 3 to 10 years before bearing fruit.

Chemical Constituents

• Thiamine, riboflavin, niacin, threonine, isoleucine, leucine, lysine, methionine, phenylalanine, tyrosine, valine, arginine, histidine, alanine, aspartic acid, glutamic acid, glycine, proline, and serine.
• Longanlactone.
• Bioactive compounds (corilagin, ellagic acid, and its conjugates, flavone glycosides, glycosides of quercetin, and kaempferol).

Traditional Medicinal Uses

• Antioxidant, cancer treatment, anti-glycated activity, antihypertensive, treat obesity, prevent and treat anxiety, immunomodulatory, treat fungus and bacteria, neuroprotective, memory-enhancing, antifatigue, stomachic, febrifuge, and vermifuge.
• The flesh of the fruit is treated as an antidote to poison.
• A dried flesh decoction is used as a tonic for insomnia and neurasthenic neurosis and as a therapy.
• The 'eye' of the Longan seed is pushed against snakebite in North and South Vietnam, hoping that the venom will be absorbed.
• The seeds are administered to counteract excessive sweating, and the pulverized kernel containing saponin, tannin, and fat helps to avoid bleeding.