Scientific name: Lansium domesticum Corr.
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 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.
Lansium domesticaton occurs in at least four cultivated forms, namely, duku, langsat (lansones), duku langsat and dokong. They differ in tree form, fruit and in fruit arrangement. A typical langsat fruit is borne in clusters of 6-10. An individual fruit is round or oval in shape, about 2.5 - 3.0cm long with a comparatively thin skin. The skin exudes latex even when it is mature. Its flesh is divided into 4 - 5 segments. Only one segment contains large, green bitter seed while others contain small seeds or are seedless. Its taste varies from sour, slightly sour to sweet. he duku fruit is round, from 2.5 - 5.0cm in diameter with a thick (6mm) dark coloured skin more leathery than duku langsat and langsat. There are usually 4 - 12 fruits per raceme. The duku langsat fruit resembles that of langsat in shape and colour except that it has a thicker skin. There are usually 5 - 25 fruits per raceme. The fruit is round or oval in shape and from 2 - 4cm in diameter. Like the langsat and duku the skin of duku langsat peels easily from the aril. In duku and duku langsat the flavour is generally very delicate and sweet. Duku langsat is native to Malaysia, Phillippines and Java where it is widely distributed. The Dokong is quite similar to the other lansium, fruit is aborate, flavour is sweet and a little samrish taste, the texture is soft and juicy. It is less asomatic compared to the other 2 lansium.
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. 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.
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.