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Fig. 53: The langsat, photographed by Dr. Walter T. Swingle, Plant Explorer for the United States Department of Agriculture.
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The tree is erect, short-trunked, slender or spreading; reaching 35 to 50 ft (10.5 to 15 m) in height, with red-brown or yellow-brown, furrowed bark. Its leaves are pinnate, 9 to 20 in (22.5-50 cm) long, with 5 to 7 alternate leaflets, obovate or elliptic-oblong, pointed at both ends, 2 3/4 to 8 in (7-20 cm) long, slightly leathery, dark-green and glossy on the upper surface, paler and dull beneath, and with prominent midrib. Small, white or pale-yellow, fleshy, mostly bisexual, flowers are home in simple or branched racemes which may be solitary or in hairy clusters on the trunk and oldest branches, at first standing erect and finally pendant, and 4 to 12 in (10-30 cm) in length.
The fruit, borne 2 to 30 in a cluster, is oval, ovoid-oblong or nearly round, 1 to 2 in (2.5-5 cm) in diameter, and has light grayish-yellow to pale brownish or pink, velvety skin, leathery, thin or thick, and containing milky latex. There are 5 or 6 segments of aromatic, white, translucent, juicy flesh (arils), acid to subacid in flavor. Seeds, which adhere more or less to the flesh, are usually present in 1 to 3 of the segments. They are green, relatively large–3/4 to 1 in (2-2.5 cm) long and 1/2 to 3/4 in (1.25-2 cm) wide, very bitter, and sometimes, if the flesh clings tightly to the seed, it may acquire some of its bitterness.
The langsat originated in western Malaysia and is common both wild and cultivated throughout the Archipelago and on the island of Luzon in the Philippines where the fruits are very popular and the tree is being utilized in reforestation of hilly areas. It is much grown, too, in southern Thailand and Vietnam and flourishes in the Nilgiris and other humid areas of South India and the fruits are plentiful on local markets. The langsat was introduced into Hawaii before 1930 and is frequently grown at low elevations. An occasional tree may be found on other Pacific islands.
The species is little known in the American tropics except in Surinam. There it is commercially grown on a small scale. Seeds were sent from Java to the Lancetilla Experimental Garden at Tela, Honduras, in 1926 and plants arrived from the same source in 1927. The trees have grown well but are usually unfruitful, occasionally having a small number of fruits. There are bearing trees in Trinidad, where the langsat was established in 1938, and a few around Mayaguez, Puerto Rico, that have been bearing well for about 60 years. There were young specimens growing on St. Croix in 1930.
Southern Florida does not have climatic and soil conditions favorable to the langsat, but the rare-fruit fancier, William Whitman, has managed to raise two bearing trees in special soil and tented for the first several years. Winter cold has caused complete defoliation and near-girdling at the base of the trunks, but the trees made good recovery. Other specimens have survived on the Lower Keys in pits prepared with non-alkaline soil. There have been attempts to maintain langsats at the University of Florida's Agricultural Research and Education Center in Homestead, but the trees have succumbed either to the limestone terrain or low temperatures.
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| Plate XXIV: LANGSAT, Lansium domesticum |
There are two distinct botanical varieties: 1) L. domesticum var. pubescens, the typical wild langsat which is a rather slender, open tree with hairy branchlets and nearly round, thick-skinned fruits having much milky latex; 2) var. domesticum, called the duku, doekoe, or dookoo, which is a more robust tree, broad-topped and densely foliaged with conspicuously-veined leaflets; the fruits, borne few to a cluster, are oblong-ovoid or ellipsoid, with thin, brownish skin, only faintly aromatic and containing little or no milky latex. The former is often referred to as the "wild" type but both varieties are cultivated and show considerable range of form, size and quality. There are desirable types in both groups. Some small fruits are completely seedless and fairly sweet.
'Conception' is a sweet cultivar from the Philippines; 'Uttaradit' is a popular selection in Thailand; 'Paete' is a leading cultivar in the Philippines.
Climate
The langsat is ultra-tropical. Even in its native territory it cannot be grown at an altitude over 2,100 to 2,500 ft (650-750 m). It needs a humid atmosphere, plenty of moisture and will not tolerate long dry seasons. Some shade is beneficial especially during the early years.
The tree does best on deep, rich, well-drained, sandy loam or other soils that are slightly acid to neutral and high in organic matter. It is inclined to do poorly on clay that dries and cracks during rainless periods, and is not at all adapted to alkaline soils. It will not endure even a few days of water-logging.
Langsats are commonly grown from seeds which must be planted within 1 or 2 days after removal from the fruit. Viability is totally lost in 8 days unless the seeds are stored in polyethylene bags at 39.2º-42.8º F (4º-6º C) where they will remain viable for 14 days.
Seedlings will bear in 12 to 20 years. Air-layering is discouraging, as the root system is weak and the survival rate is poor after planting out. Shield-budding has a low rate of success. Cleft- and side-grafting and approach-grafting give good results. The budwood should be mature but not old, 2 1/2 to 3 1/2 in (6.5-9 cm) long, 1/4 to 3/4 in (6-20 mm) thick, and it is joined to rootstock of the same diameter about 2 1/2 to 4 in (6.5-10 cm) above the soil. Some preliminary experiments have been conducted in Puerto Rico with hormone-treated cuttings under intermittent mist. Whitman found that a potted cutting 3 to 4 in (7.5-10 cm) long, will root if covered with a clear plastic bag.
The trees are spaced 25 to 33 ft (8-10 m) apart in orchards. In the Philippines they are frequently planted around the edges of coconut plantations. Generally, the langsat is casually grown in dooryards and on roadsides and receives no cultural attention. Regular irrigation results in better fruit size and heavier crops. Whitman has demonstrated that thrice-yearly applications of a 6-6-6 fertilizer formula with added minor elements result in good growth, productivity and high quality fruits even in an adverse environment.
Langsats in Malaya generally bear twice a year-in June and July and again in December and January or even until February. In India, the fruits ripen from April to September but in the Philippines the season is short and most of the fruits are off the market in less than one month.
Trees in the Nilgiris average 30 lbs (13.5 kg) of fruits annually. In the Philippines, a productive tree averages 1,000 fruits per year.
Langsats are perishable and spoil after 4 days at room temperature. They can be kept in cold storage for 2 weeks at 52º to 55º F (11.11º-12.78º C) and relative humidity of 85-90%. Sugar content increases over this period, while acidity rises only up to the 7th day and then gradually declines.
Fruits treated with fungicide and held at 5% 0 and zero CO2 and 58º F (14.44º C) with 85% to 90% humidity, have remained in good condition for more than 2 weeks. High C02 promotes browning and elevates acidity.
Waxing reduces weight loss, increases sweetness, but causes browning over at least half the surface within 5 days in storage.
In Puerto Rico, young langsat trees have been defoliated by the sugarcane root borer, Diaprepes abbreviatus. Scale insects, especially Pseudaonidia articulatus and Pseudaulacaspis pentagona, and the red spider mite, Tetranychus bimaculatus, are sometimes found attacking the foliage, and sooty mold is apt to develop on the honeydew deposited by the scales. Rats gnaw on the branchlets and branches and the mature fruits.
Anthracnose caused by Colletotrichum gloeosporioides is evidenced by brown spots and other blemishes on the fruit and peduncle and leads to premature shedding of fruits.
Canker which makes the bark become rough and corky and flake off has appeared on langsats in Florida, Hawaii and Tahiti. It was believed to be caused by a fungus, Cephalosporium sp., and larvae of a member of the Tineidae have been observed feeding under the loosened bark. However, other fungi, Nectria sp. (perfect stage of Volutella sp.) and Phomopsis sp. are officially recorded as causes of stem gall canker on the langsat in Florida.
The peel of the langsat is easily removed and the flesh is commonly eaten out-of-hand or served as dessert, and may be cooked in various ways.
Varieties with much latex are best dipped into boiling water to eliminate the gumminess before peeling.
The peeled, seedless or seeded fruits are canned in sirup or sometimes candied.
| Food Value Per 100 g of Edible Portion* | |
| Moisture | 86.5 g |
| Protein | 0.8 g |
| Carbohydrates | 9.5 g |
| Fiber | 2.3 g |
| Calcium | 20.0 mg |
| Phosphorus | 30.0 mg |
| Carotene (Vitamin A) | 13.0 I.U. |
| Thiamine | 89 mcg |
| Riboflavin | 124 mcg |
| Ascorbic Acid | 1.0 mg |
| Phytin | 1.1 mg (dry weight) |
The edible flesh may constitute 60% of the fruit.
An arrow poison has been made from the fruit peel and the bark of the tree. Both possess a toxic property, lansium acid, which, on injection, arrests heartbeat in frogs. The peel is reportedly high in tannin. The seed contains a minute amount of an unnamed alkaloid, 1% of an alcohol-soluble resin, and 2 bitter, toxic principles.
Peel: The dried peel is burned in Java, the aromatic smoke serving as a mosquito repellent and as incense in the rooms of sick people.
Wood: The wood is light-brown, medium-hard, fine-grained, tough, elastic and durable and weighs 52.3 lbs/ cu ft. It is utilized in Java for house posts, rafters, tool handles and small utensils. Wood-tar, derived by distillation, is employed to blacken the teeth.
Medicinal Uses: The fresh peel contains 0.2% of a light-yellow volatile oil, a brown resin and reducing acids. From the dried peel, there is obtained a dark, semi-liquid oleoresin composed of 0.17 % volatile oil and 22% resin. The resin is non-toxic and administered to halt diarrhea and intestinal spasms; contracts rabbit intestine in vitro.
The pulverized seed is employed as a febrifuge and vermifuge. The bark is poulticed on scorpion stings. An astringent bark decoction is taken as a treatment for dysentery and malaria. Leaves may be combined with the bark in preparing the decoction. The leaf juice is used as eye-drops to dispel inflammation.