Nephelium (PROSEA Timbers)

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Plant Resources of South-East Asia
Introduction
List of species


Nephelium L.


Protologue: Mant. pl. 1: 18 (1767).
Family: Sapindaceae
Chromosome number: x = 11; N. lappaceum: 2n = 22

Vernacular names

  • Rambutan (En, trade name)
  • Brunei: buah hitam, buah satu inchi
  • Malaysia: meritam (Sabah), sibu (Sarawak)
  • Thailand: ngoh (central)
  • Vietnam: chôm chôm.

Origin and geographic distribution

Nephelium comprises 22 species which occur from India (Assam), peninsular Burma (Myanmar), Indo-China, southern China, Hainan and Thailand to Peninsular Malaysia (10 species), Sumatra (8), western Java (3), Borneo (8), the Philippines (4) and Sulawesi (1).

Uses

The wood of Nephelium is used for general construction (e.g. planking, beams) and furniture. It has also been applied for tool handles because of its toughness, and as firewood.

The sarcotesta of the fruits of many species - including the well-known, cultivated rambutan (N. lappaceum) - is edible, but the sarcotesta of some species is too small or too acid to be edible. The seeds contain an oil formerly used for illumination and a fat used formerly for soap and candles. The boiled or roasted seeds have been used in a beverage. The seeds of some Nephelium species are said to be poisonous. The fruit rind and occasionally the roots are used for medicinal purposes. An inferior black dye has been prepared from the shoots and the leaves.

Production and international trade

As many Nephelium species yield edible fruits and trees are generally fairly small and too crooked to produce sawn timber, trees are seldom cut.

Properties

Nephelium yields a medium-weight to heavy hardwood with a density of 615-1110 kg/m3 at 15% moisture content. Heartwood brown or pale purple-red or pale greyish-brown, sometimes distinct from the narrow sapwood; grain slightly interlocked to interlocked; texture moderately fine and even; pale zig-zag markings caused by parenchyma present on longitudinal surfaces. Growth rings indistinct or marked by marginal parenchyma; vessels moderately small to medium-sized, solitary or in radial multiples of 2-4, with occasional pale-coloured yellow-brown deposits; parenchyma moderately abundant to abundant, paratracheal aliform and confluent, and apotracheal in narrow marginal or seemingly marginal bands, visible to the naked eye; rays extremely fine to very fine, only visible with a hand lens; ripple marks absent.

The wood of N. lappaceum is liable to splitting during seasoning. It is moderately hard to very hard, strong and tough. The wood is easy to work and can be finished well. It is durable under cover and generally resistant to insect attacks, but susceptible to fungal attack.

The average fibre length of wood of N. lappaceum is 1.07 mm.

See also the table on microscopic wood anatomy.

Botany

  • Evergreen, dioecious or sometimes monoecious, small to fairly large trees up to 35(-44) m tall, rarely shrubs; bole usually fairly slender and straight or rather crooked, up to 90(-140) cm in diameter, occasionally fluted, sometimes with buttresses up to 2(-4) m high; bark surface smooth to slightly flaking or sometimes dippled, often lenticellate, inner bark brown to orange or red.
  • Leaves arranged spirally, paripinnate, 1-foliolate or 1-5(-18)-jugate, exstipulate; leaflets alternate or occasionally opposite, often glaucous and with domatia below.
  • Flowers in an axillary or terminal, thyrsoid inflorescence, unisexual (sometimes at least functionally so); sepals (4-)5(-6), free to connate in the lower half; petals 5(-6), sometimes 1-4 reduced or all absent, shorter than the calyx, clawed and with a bilobed scale inside; disk entire. Male flowers with 4--10 stamens. Female flowers with a superior, (1-)2(-4)-locular, warty ovary with 1 ovule in each cell, style 1.
  • Fruit a 1(-3)-lobed, partly to irregularly dehiscing capsule, generally with a warty to spiny wall.
  • Seed almost entirely covered by a sarcotesta.
  • Seedling with hypogeal germination; cotyledons not emergent; hypocotyl not elongated; first pair of leaves opposite, paripinnate, subsequent ones with increasing numbers of leaflets. Seedlings of N. juglandifolium and N. ramboutan-ake differ in being semi-hypogeal and in having tardily emergent cotyledons.

Ectomycorrhizae have been observed in Nephelium. Growth is in distinct flushes. Tree architecture is according to Scaronne's model, characterized by an indeterminate trunk bearing tiers of orthotropic branches which branch sympodially as a result of terminal flowering. N. lappaceum flowers 5-6 years after sowing. Flowering is initiated by a distinct dry spell and is reported to be annually. However, observations in Peninsular Malaysia show that most Nephelium species flower only once every 4 years. Apparently they need a definite, but not excessive, dry season for good flowering and heavy fruit set. Flowers are pollinated by insects, mainly bees. Most species are effectively dioecious since little or no viable pollen is produced in flowers appearing to be bisexual. The fruits take about 3 months to mature. They are eaten and dispersed by primates.

Identification without fruits is almost impossible. N. cuspidatum is highly variable with 6 varieties. N. lappaceum is subdivided into 3 varieties.

Ecology

Timber-yielding species of Nephelium are generally found as middle storey trees in evergreen, lowland or sometimes montane, primary or sometimes secondary rain forest on hills and ridges, up to 600(-1950) m altitude. The habitat varies between species, but most are found in well-drained locations on sandy to loamy or clayey soils or on limestone, although several occur on river banks and in swamps. N. daedaleum has been reported from kerangas, and N. lappaceum from peat soils. N. papillatum is typical of montane forest.

Silviculture

Nephelium is usually propagated by seed, but in commercial fruit production of N. lappaceum vegetative propagation (budding) is used. The seed of Nephelium should be sown immediately after collection. When stored, the seed should be kept in polyethylene bags at 20°C in sawdust moistened with juice from the fruits, as the juice inhibits germination. In this way, seed can be stored for up to 4 weeks. Germination trials in Malaysia included the following species: N. costatum, N. cuspidatum, N. hamulatum, N. juglandifolium, N. lappaceum, N. maingayi, N. ramboutan-ake and N. uncinatum. In general germination was good and rapid, being 85--100% in (7-)13-52(-58) days after sowing, and no important differences were found between seed sown with or without adhering pulp. The germination rate of seed of N. uncinatum, however, was only about 40%, regardless of whether the seed was sown with or without pulp. It may be necessary to inoculate the planting stock with ectomycorrhizae before planting out. In a 50-ha plot in natural forest at Pasoh (Peninsular Malaysia), a total of 280 Nephelium trees with a diameter over 10 cm were present.

Genetic resources and breeding

Several of the minor fruit trees of Nephelium are of interest for cultivation and breeding. N. lappaceum is especially promising for breeding. Germplasm collections in South-East Asia are now being enriched with these minor species.

Prospects

Timber production is not very important within Nephelium and is unlikely to increase in the near future. Some species, notably N. ramboutan-ake, may become important as fruit trees.

Literature

151, 158, 163, 191, 209, 238, 267, 341, 436, 438, 543, 595, 632, 690, 694, 825, 829, 831, 861, 934, 974, 981, 987, 1038, 1048, 1164, 1219, 1221, 1242, 1259.

Selection of species

Author

T. Uji

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