Tree Form of duku and langsat is a slender tree, 10 to 20 metres high with a straight trunk, slender upright branches, and an irregular or rounded crown. Duku tends to be less tall and has a wider crown than langsat. Leaves are large and divided into 5 to 7 alternately placed leaflets and one terminal leaflet. Leaflets are dark green and shiny above, light green and dull beneath and measure 150 to 200 mm long by 60 to 100 mm wide. The leaves are faintly hairy underneath (langsat) or hairless (duku). The Flowers are many-flowered inflorescences (racemes) are borne either singly or in groups of 2 to 5 on the trunk and large branches and are thus essentially cauliflorous. The racemes, erect at first but later drooping as the flowers and fruits mature, are 100 to 300 mm long, being smallest in duku. Flowers are about 12 mm wide and number about 20 to 30 arranged on a spike. Although unbranched, there are usually several spikes emanating from the branch or trunk in one spot. Flowers are perfect and sub sessile. There are 5 sepals and 5 petals which are rounded and imbricate. The stamens are united in a tube with 10 anthers on each flower. The style on top of the tiny ovary is very short and is capped with a 5-lobed stigma. Flowers have a sweet smell.
Duku and Langsat fruits are slightly longer than wide in langsat and about 30 or 40 mm long. In duku they are round and 40 to 50 mm in diameter. There are commonly 15 to 25 fruits per spike in langsat and 4 to12 in duku. Another variant or sub species of the langsat grown in Indonesia called the kokosan (very acid to taste) has up to 50 very small fruit on each spike (Anon, 1975). Fruits of both langsat and duku have very short stalks, less than 4 mm long. The skin ripens to a greyish buff or pale muddy yellow colour with brown blemishes. The blemishes appear as the fruit ripens, and extend to cover the fruit when it is past maturity. In some forms of duku the fruits are pink. The skin may be very thin in langsat, or just less than 7 mm thick in duku, and is dull and covered with minute, short pale hairs. In langsat, (but not in duku) there is a milky sticky latex in the skin. The skin peels easily and cleanly from the flesh. The flesh of both is white, translucent and juicy. In langsat, flavour varies from sweet to sour, but in duku it is very delicate and sweet. The flesh separates easily into 5 different-sized segments. In duku most fruits have no seeds, but when present are up to 25 mm long by 12 to 18 mm wide. In langsat there may be 1 to 5 seeds in each fruit, each up to 18 mm length. Seeds have a thin green coating, are extremely bitter, and are firmly attached to the flesh. Fruits are very refreshing and large quantities can be eaten at one time without feeling particularly full - a fact confirmed by the writer whilst working in Borneo. Fruits are most commonly eaten fresh. In Malaysia the seedless or less seedy duku are skinned and bottled in syrup. The product is said to be delicious. In the Philippines, seedless segments can be frozen. The segments are placed in 70% syrup, frozen at minus 40° C and stored at minus 8° C. Frozen fruit remain white with no surface discolouration and the texture is very good. Whole fruits when frozen alone or in syrup are very palatable, but the skin quickly turns brown. Thanks for reading this article.
Source: Department of Agriculture (Horticulture Division)