Nephelium glabrum Cambess.

Dimocarpus longan is handsome, erect, 9-12 m in height and 14 m in width, with rough-barked trunk 76.2 cm thick and long, spreading, slightly drooping, heavily foliaged branches. Leaves evergreen, alternate, paripinnate, 4-10 opposite leaflets, elliptic, ovate-oblong or lanceolate, blunt-tipped; 10-20 cm long and 3.5-5 cm wide; leathery, wavy, glossy-green on the upper surface, minutely hairy and greyish-green beneath. New growth is wine-colored and showy. Flowers pale-yellow, 5-6-petalled, hairy-stalked, larger than those of the closely related species, Litchi chinensis (lychee), are borne in upright terminal panicles, male and female mingled. Fruits, globose in drooping clusters, 1.25-2.5 cm in diameter, with thin, brittle, yellow-brown to light reddish-brown rind, more or less rough (pebbled), the protuberances much less prominent than those of the lychee. The flesh (aril) is mucilaginous, whitish, translucent, somewhat musky, sweet, but not as sweet as that of the lychee and with less "bouquet". Seed round, jet-black, shining, with a circular white spot at the base, giving it the aspect of an eye.

Fruits ripen from early to mid-August in China, August and September in Florida.

The longan thrives best on a rich sandy loam and nearly as well on moderately acid, somewhat organic, sand. It also grows to a large size and bears heavily in oolitic limestone. In organic muck soils, blooming and fruiting are deficient.

The longan is native to southern China, in the provinces of Kwangtung, Kwangsi, Schezwan and Fukien, between elevations of 150-450 m. It thrives much better on higher ground than the lychee and endures more frost. It is rarely found growing along the dykes of streams as is the lychee but does especially well on high ground near ponds. The longan appears in these regions more often but it, too, cannot stand heavy frosts. After a long period of cool weather over the 3 winter months, with no frost, longan trees bloom well. Blooming is poor after a warm winter.

In Indian literature, it is averred that the longan is native not only to China but also to southwestern India and the forests of upper Assam and the Garo hills, and is cultivated in Bengal and elsewhere as an ornamental and shade tree. It is commonly grown in former Indochina (Thailand, Cambodia, Laos and Vietnam) and in Taiwan. The tree grows but does not fruit in Malaysia and the Philippines. There are many of the trees in Reúnion and Mauritius. The longan was introduced into Florida from southern China by the United States Department of Agriculture in 1903 and has flourished in a few locations but never became popular. A longan tree flourished in the Atkins Garden in Cuba and seedlings were distributed but found to fruit irregularly and came to be valued mostly for their shade and ornamental quality.

Most longan trees are grown from seed. After drying in the shade for 4 days, they should be planted without delay, but no more than 2 cm deep, otherwise they may send up more than one sprout. Germination takes place within 7-10 days. The seedlings are transplanted to shaded nursery rows the following spring and set in the field 2-3 years later during winter dormancy. Vegetative propagation is undertaken, by means of inarching, nearly always onto 'Wu Yuan' trees 3-5 years old and 1.5-1.8 m high. The union is made no less than 1.2 m from the ground because it is most convenient. Grafting is uncommon, whip-grafting has given 80% success in Taiwan. Air layering is done frequently. Air-layers bear in 2-3 years after planting.

A tree can be converted to a preferred cultivar by cutting it drastically back and veneer-grafting the new shoots. In China, if the longan is raised on the lowlands it is always put on the edges of raised beds. On high ground, the trees are placed in pre-enriched holes on the surface. The trees are fertilized after the fruit harvest and during the blooming season, at which time the proportion of nitrogen is reduced. Fresh, rich soil is added around the base of the trees year after year. The longan needs an adequate supply of water and can even stand brief flooding, but not prolonged drought. Irrigation is necessary in dry periods. Pruning of many flower-bearing twigs where 3/4 of the flower spikes in the cluster are removed is essential. Later, the fruit clusters are also thinned, in order to increase the size and quality of the fruits. In China, full-grown trees given sufficient room–at least 12 m apart–may yield 180-225 kg in good years. Crops in Florida from trees 6 m tall, have varied from light 22.5-45 kg–to medium–68-113 kg, and heavy–135-225 kg. Rarely such trees may produce 272-317 kg. Larger trees have larger crops but if the trees become too tall harvesting is too difficult, and they should be topped. A serious problem with the longan is its irregular bearing–often one good year followed by 1 or 2 poor years.

The longan is relatively free of pests and diseases. At times, there may be signs of mineral deficiency which can be readily corrected by supplying minor elements in the fertilization program.

Seeds are recalcitrant. They lose viability at 18 % moisture content. There is 70 % survival after 7 weeks storage with anesthetic substances such as moist storage at 8-10 deg C with 100 % relative humidity and with 80 % nitrous oxide + 20 % oxygen, but no viability when water is used; and 67 % germination after 250 days moist storage in moist (20 % moisture content) perlite + 4 % chlorthalonil, at 15 deg C.

Shade or shelter: The longan is cultivated in Bengal and elsewhere as a shade tree. Ornamental: The tree is widely cultivated as an ornamental.

Food: Longans are much eaten fresh, out-of-hand, but some have maintained that the fruit is improved by cooking. In China, the majority are canned in syrup or dried. The canned fruits were regularly shipped from Shanghai to the United States in the past. Today, they are exported from Hong Kong and Taiwan. For drying, the fruits are first heated to shrink the flesh and facilitate peeling of the rind. Then the seeds are removed and the flesh dried over a slow fire. The dried product is black, leathery and smoky in flavor and is mainly used to prepare an infusion drunk for refreshment. Fuel: The seeds and the rind are burnt for fuel. The wood is not highly valued for fuel. Timber: While the tree is not often cut for timber, the wood is used for posts, agricultural implements, furniture and construction. The heartwood is red, hard, and takes a fine polish. Alcohol: A liqueur is made by macerating the longan flesh in alcohol. Medicine: The flesh of the fruit is administered as a stomachic, febrifuge and vermifuge, and is regarded as an antidote for poison. A decoction of the dried flesh is taken as a tonic and treatment for insomnia and neurasthenic neurosis. In both North and South Vietnam, the "eye" of the longan seed is pressed against a snakebite in the belief that it will absorb the venom. Leaves and flowers are sold in Chinese herb markets but are not a part of ancient traditional medicine. The leaves contain quercetin and quercitrin. Dried flowers are exported to Malaysia for medicinal purposes. The seeds are administered to counteract heavy sweating and the pulverized kernel, which contains saponin, tannin and fat, serves as a styptic. Other products: The seeds, because of their saponin content, are used like soapberries (Sapindus saponaria L.) for shampooing the hair.