Tropical Plant "Longan"
Dimocarpus longan

• Longan Description
• Longan Origin and Distribution
• Longan Varieties
• Longan Climate
• Longan Soil
• Longan Propagation
• Longan Culture
• Longan Keeping Quality
• Longan Pests and Diseases
• Longan Food Uses
• Longan Other Uses

Longan Description

The longan tree is handsome, erect, to 30 or 40 ft (9-12 m) in height and to 45 ft (14 m) in width, with rough-barked trunk to 2 1/2 ft (76.2 cm) thick and long, spreading, slightly drooping, heavily foliaged branches. The evergreen, alternate, paripinnate leaves have 4 to 10 opposite leaflets, elliptic, ovate-oblong or lanceolate, blunt-tipped; 4 to 8 in (10-20 cm) long and 1 3/8 to 2 in (3.5-5 cm) wide; leathery, wavy, glossy-green on the upper surface, minutely hairy and grayish-green beneath. New growth is wine-colored and showy.

The pale-yellow, 5- to 6-petalled, hairy-stalked flowers, larger than those of the lychee, are borne in upright terminal panicles, male and female mingled. The fruits, in drooping clusters, are globose, 1/2 to 1 in (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". The seed is round, jet-black, shining, with a circular white spot at the base, giving it the aspect of an eye.

Longan Origin and Distribution

The longan is native to southern China, in the provinces of Kwangtung, Kwangsi, Schezwan and Fukien, between elevations of 500 and 1,500 ft (150-450 m). Groff wrote: "The lungan, not so highly prized as the lychee, is nevertheless usually found contiguous to it .... 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 lungan is more seldom grown under orchard conditions than is the lychee.

There is not so large a demand for the fruit and the trees therefore more scattered although one often finds attractive groups of lungan." Groff says that the longan was introduced into India in 1798 but, 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 Malaya 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. There was a young tree growing at the Agricultural Station in Bermuda in 1913. A tree planted at the Federal Experiment Station in Mayaguez, Puerto Rico, was 10 ft (3 m) high in 1926, 23 ft (7 m) in 1929. 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. In Hawaii, the longan was found to grow faster and more vigorously than the lychee but the fruit is regarded there as less flavorful than the lychee.

Longan Varieties

It seems that the type of longan originally brought to the New World was not one of the best, having aroused so little interest in the fruit. Groff stated that the leading variety of Fukien was the round-fruited 'Shih hsía', the "Stone Gorge Lungan" from P'ing Chou. There were 2 types, one, 'Hei ho shih hsia', black-seeded, and 'Chin ch' i ho shih hsia', brown-seeded. This variety did not excel in size but the flesh was crisp, sweeter than in other varieties, the seed small and the dried flesh, after soaking in water, was restored almost to fresh condition.

None of the other 4 varieties described by Groff has any great merit.

'Wu Yuan' ("black ball") has small, sour fruit used for canning. The tree is vigorous and seedlings are valued as rootstocks. 'Kao Yuan' is believed to be a slightly better type of this variety and is widely canned.

'Tsao ho' ('Early Rice') is the earliest variety and a form called 'Ch'i chin tsao ho' precedes it by 2 weeks. In quality, both are inferior to 'Wu Yuan'.

'She p' i' ('Snake skin') has the largest fruit, as big as a small lychee and slightly elongated. The skin is rough, the seed large, some of the juice is between the rind and the flesh, and the quality is low. Its only advantage is that it is very late in season.

'Hua Kioh' ('Flower Skin'), slightly elongated, has thin, nearly tasteless flesh, some of the juice is between the rind and the flesh, and the overall quality is poor. It is seldom propagated vegetatively.

There are no "chicken- tongue" (aborted seed) varieties in China.

There are 2 improved cultivars grown extensively in Taiwan-'Fukien Lungan' ('Fukugan') was introduced from Fukien Province in mainland China. The other, very similar and possibly a mutant of 'Fukien', is 'Lungan Late', which matures a month later than 'Fukien'.

In 1954, William Whitman of Miami introduced a superior variety of longan, the 'Kohala', from Hawaii. It began to bear in 1958. The fruit is large for the species, the seed is small, and the flesh is aromatic, sweet and spicy. The tree produces fairly good crops in midsummer. One hundred or more air-layers have been brought by air from Hawaii and planted at various locations in southern Florida and in the Bahamas.

A seedling planting and selection program was started in 1962 at the USDA Subtropical Horticulture Research Unit, Miami. The plants were all open-pollinated seedlings of the canning variety, 'Wu Yuan', brought in from Canton in 1930 as P.I. #89409. Some set fruit in 1966 and 1967 but more of them in 1968. Evaluation of these and other acquisitions continues. Included in the study are M-17886, 'Chom Poo Nuch', and M-17887, 'E-Haw'.

Longan Climate

Lungan is found growing at higher latitudes and higher altitudes than the lychee.On the higher elevations of the mountainous regions which are subject to frost the lychee is seldom grown. The longan appears in these regions more often but it, too, cannot stand heavy frosts.

The longan's range in Florida extends north to Tampa on the west coast and to Merritt Island on the east coast. Still, small trees suffer leaf-and twig-damage if the temperature falls to 31º or 30º F (-0.56º--l.11º C) and are killed at just a few degrees lower. Larger trees show leaf injury at 27º to 28º F (-2.78º--2.22º C), small branch injury at 25º to 26º F (-3-89º--3.33º C), large branch and trunk symptoms at 24º F (-4.44º C) and sometimes fail to recover.

On the other hand, 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.

Longan Soil

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.

Longan Propagation

Most longan trees have been grown from seed. The seeds lose viability quickly. After drying in the shade for 4 day, they should be planted without delay, but no more than 3/4 in (2 cm) deep, otherwise they may send up more than one sprout. Germination takes place within a week or 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.

In Kwangtung Province, when vegetative propagation is undertaken, it is mostly by means of inarching, nearly always onto 'Wu Yuan' trees 3-5 years old and 5 to 6 ft (1.5-1.8 m) high. The union is made no less than 4 ft (1.2 m) from the ground because it is most convenient. Nevertheless, the point of attachment remains weak and needs to be braced with bamboo to avoid breaking in high winds.

Grafting is uncommon and when it is done, it is a sandwich graft on longan rootstock, 3 or 4 grafts being made successively, one onto the beheaded top of the preceding one, in the belief that it makes the graft wind-resistant and that it induces better size and quality in the fruit.

Conventional modes of grafting have not been successful in Florida, but whip-grafting has given 80% success in Taiwan. Air-layering is frequently done in Fukien Province and was found a feasible means of distributing the 'Kohala' from Hawaii. Air-layers bear in 2 to 3 years after planting. A tree can be converted to a preferred cultivar by cutting it drastically back and veneer-grafting the new shoots.

Longan Culture

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.

An important operation is the pruning of many flower-bearing twigs-3/4 of the flower spikes in the cluster being removed. Later, the fruit clusters are also thinned, in order to increase the size and quality of the fruits.

Generally, the trees are planted too close together, seriously inhibiting productivity when they become overcrowded. In China, full-grown trees given sufficient room-at least 40 ft (12 m) apart-may yield 400 to 500 lbs (180-225 kg) in good years. Crops in Florida from trees 20 ft (6 m) tall and broad, have varied from light-50-100 lbs (22.5-45 kg)-to medium-150-250 lbs (68-113 kg), and heavy-300-500 lbs (135-225 kg). Rarely such trees may produce 600-700 lbs (272-317 kg). Larger trees have larger crops but if the trees become too tall harvesting is too difficult, and they should be topped. Harvesters, working manually from ladders, or using pruning poles cut the entire cluster of fruit with leaves attached.

A serious problem with the longan is its irregular bearing-often one good year followed by 1 or 2 poor years. Another handicap is the ripening season-early to mid-August in China, which is the time of typhoons; August and September in Florida which is during the hurricane season. Rain is a major nuisance in harvesting and in conveying the fruit to market or to drying sheds or processing plants.

Longan Keeping Quality

At room temperature, longans remain in good condition for several days. Because of the firmer rind, the fruit is less perishable than the lychee.

Preliminary tests in Florida indicate that the fruit can be frozen and will not break down as quickly as the lychee when thawed.

Longan Pests and Diseases

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.

Longan Food Uses

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 sirup 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.

Longan Other Uses

Seeds and rind: The seeds, because of their saponin content, are used like soapberries (Sapindus saponaria L.) for shampooing the hair. The seeds and the rind are burned for fuel and are part of the payment of the Chinese women who attend to the drying operation.

Wood: 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. It is not highly valued for fuel.

Medicinal Uses: 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. Burkill says that the 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.