Though a close relative of the lychee and an equally desirable fruit, this member of the Sapindaceae is not nearly as well-known. Botanically, it is Nephelium lappaceum L. (syns. Euphoria nephelium DC.; Dimocarpus crinita Lour.). In the vernacular, it is generally called rambutan (in French, ramboutan or ramboutanier; in Dutch, ramboetan); occasionally in India, ramboostan. To the Chinese it is shao tzu, to Vietnamese, chom chom or vai thieu; to Kampucheans, ser mon, or chle sao mao. There are other local names in the various dialects of southeast Asia and the East Indies.

The rambutan tree reaches 50 to 80 ft (15-25 m) in height, has a straight trunk to 2 ft (60 cm) wide, and a dense, usually spreading crown. The evergreen leaves are alternate, pinnately compound, 2 3/4 to 12 in (7-30 cm) long, with reddish rachis, hairy when young, and 1 to 4 pairs of leaflets, subopposite or alternate, elliptic to oblong-elliptic, or rather obovate, sometimes oblique at the base; slightly leathery; yellowish-green to dark-green and somewhat dull on the upper surface, yellowish or bluish-green beneath; 2 to 8 in (5-20 cm) long, 1 to 4 1/3 in (2.5-11 cm) wide, the 6 to 15 pairs of principal veins prominent on the underside. The small, petalless flowers, of three kinds: males, hermaphrodite functioning as males, and hermaphrodite functioning as females, are borne in axillary or pseudo-terminal, much branched, hairy panicles. The fruit is ovoid, or ellipsoid, pinkish-red, bright-or deep-red, orange-red, maroon or dark-purple, yellowish-red, or all yellow or orange-yellow; 1 1/3 to 3 1/8 in (3.4-8 cm) long. Its thin, leathery rind is covered with tubercles from each of which extends a soft, fleshy, red, pinkish, or yellow spine 1/5 to 3/4 in (0.5-2 cm) long, the tips deciduous in some types. The somewhat hairlike covering is responsible for the common name of the fruit, which is based on the Malay word "rambut", meaning "hair".

Within is the white or rose-tinted, translucent, juicy, acid, subacid or sweet flesh, 1/6 to 1/3 in (0.4-0.8 cm) thick, adhering more or less to the ovoid or oblong, somewhat flattened seed, which is 1 to 1 1/3 in (2.5-3.4 cm) long and 2/5 to 3/5 in (1-1.5 cm) wide. There may be 1 or 2 small undeveloped fruits nestled close to the stem of a mature fruit.

Ordinarily, the fruits must be gotten to local markets within 3 days of picking before shriveling and decay begin. Fungicidal applications and packing in perforated polyethylene bags have extended fresh life somewhat. Weight loss has been reduced by packing in sawdust, or coating with a wax emulsion. Storing in sealed polyethylene bags at 40º F (10º C) and 95% relative humidity has preserved the fruits in fresh condition for 12 days. Some cultivars, as noted, keep better than others.

Origin

Nephelium lappaceum Linn., Sapindaceae, is native to Malaysia and Indonesia. Rambutan, a tropical relative of the lychee (Litchi chinensis Sonn.), is grown in Southeast Asia, Australia, South America, and Africa, but only exported from Malaysia and Thailand (Laksmi et al. 1987).

Foliage

Larvae of the leaf roller, adoxophytes privatana walk, roll and feed on young leaves. It can be controlled chemically. The are three weevil pests - apogonia SPP., adoretus SPP and Hypomeces Squamosus which feed on and cut leaves. They are only active at night. This can be chemically controlled by spraying with Trichlorphon or BHC.

Flowers

The small 0.1 to 0.2 in (2.5 to 5 mm), apetalous, discoidal flowers occur in erect terminal clusters (panicles) about 12 in (30 cm) long. Rambutan trees are either male (producing only staminate flowers and, hence, produce no fruit), hermaphroditic (producing flowers that are only functionally female), or hermaphroditic (producing flowers that are female with a small percentage of male flowers). The latter is most commonly found in cultivar selections (Almeyda, et al., 1979; Chin and Phoon, 1982; Tindall, 1994). Cultivars that produce only functionally female flowers require the presence of male trees. Male trees are seldom found as vegetative selection has favored hermaphroditic clones that produce a high proportion of functionally female flowers and a much lower number of flowers that produce pollen. There are over 3000 greenish_white flowers in male panicles, each with five to seven anthers and a non-functional ovary. Male flowers have yellow nectaries and 5-7 stamens. There are about 500 greenish_yellow flowers in each hermaphroditic panicle. Each flower has six anthers, usually a bi_lobed stigma, and one ovule in each of its two sections (locules) (Free, 1993; Tindall, 1994). The flowers are receptive for about one day but may persist if pollinators are excluded (Tindall, 1994).

In Malaysia, Rambutan flowers from March to July and again between July and November, usually in response to rain following a dry period. Flowering periods differ for other localities. Most, but not all, flowers open early in the day. Up to 100 flowers in each female panicle may be open each day during peak bloom. Initial fruit set may approach 25 percent but a high level of abortion contributes to a much lower level of production at harvest (1-3%). The fruit matures 15 to 18 weeks after flowering (Tindall, 1994).

Both male and female flowers are faintly sweet scented and have functional nectaries at the ovary base. Female flowers produce 2-3 times more nectar than male flowers. Nectar sugar concentration ranges between 18 and 47 percent and is similar between the flower types (Free, 1993; Lim, 1992; Tindall, 1994). Rambutan is an important nectar source for bees in Malaysia (Phoon, 1983).

Fruits

The red, pink, or yellow fruit, about the size of a small egg, consists of a single seed covered by a translucent, juicy but firm, sweet aril or pulp. The fruit are usually sold fresh, used in making jams and jellies, or canned. Evergreen Rambutan trees with their abundant colored fruit make beautiful landscape specimens.

Info Source : International Tropical Fruits Network