5337

5(3): Timber trees; Lesser-known timbers

Elateriospermum Blume

Bijdr. fl. Ned. Ind. 12: 620 (1826).

EUPHORBIACEAE

x = unknown; 2n = unknown

Tapus (trade name). Indonesia: kedui (Sumatra), tapos (Sundanese). Malaysia: perah (general), dungku, kelampai (Sarawak). Thailand: pee-ra, pra (peninsular).

Elateriospermum is a monotypic genus occurring in peninsular Thailand, Peninsular Malaysia, Sumatra, Java and Borneo. Its only species is E. tapos Blume.

The wood of E. tapos is suitable for medium and heavy construction under cover and parquet flooring. When treated it can be applied for outdoor construction and in contact with the ground, as railway sleepers and fence posts. It has been the most popular wood for handles of tapping knives, especially in Peninsular Malaysia. The wood makes an excellent firewood.
The tree is sometimes cultivated as an ornamental. The seeds are edible when boiled, roasted, or pounded and fermented; sometimes they are made into small toys. The fermented paste has been used for fish bait.

Fair supplies of E. tapos are available from Peninsular Malaysia but supplies are small elsewhere. The wood is mainly used on a local scale.

E. tapos yields a medium-weight to heavy hardwood with a density of 730-1230 kg/m³ at 15% moisture content. Heartwood dark brown with a red tinge, streaked, sharply differentiated from the about 5 cm wide, pale brown sapwood; grain straight or only shallowly interlocked; texture moderately fine to medium and even; corewood may be darker; heartwood lustrous. Growth rings usually indistinct, occasionally darker coloured layers suggest growth rings; vessels medium-sized to moderately large, solitary and in radial multiples of 2-4, sometimes radially aligned, open or filled with yellow-white, gum-like deposits or blocked by sclerotic tyloses; parenchyma abundant, apotracheal in narrow regularly spaced bands, visible to the naked eye; rays very fine to moderately fine, visible with a hand lens; ripple marks absent.
Shrinkage upon seasoning is moderate to high. The wood air dries fairly fast with no defects; boards 13 mm and 38 mm thick take respectively 2.5 and 4 months to air dry. There is a high risk of sap-stain and a moderate risk of insect attack during seasoning. Splitting and surface checking may only be slight. The wood is very hard and strong. It is difficult to saw, as saw teeth gum up rapidly. It should be treated immediately after sawing, to prevent stain. It is difficult to bore, but moderately easy to plane, producing a smooth finish. It is not durable. In a graveyard test stakes were destroyed in 1-6.5 years and only 5% were serviceable after 2 years; the dark coloured corewood may be more durable. The wood is easily treated with preservatives and an absorption of a mixture of 50% creosote and 50% fuel oil of 90-200 kg/m³ has been determined using the open tank method. The corewood, however, is very difficult to treat. The wood is susceptible to termite attack. The sapwood is susceptible to Lyctus.
The gross energy value of the wood is 19 695-20 640 kJ/kg. The mean fibre length of Indonesian material is 1.502 mm. The fresh seeds contain hydrocyanic acid.
See also the tables on microscopic wood anatomy and wood properties.

A deciduous or semi-deciduous, monoecious, small to medium-sized tree up to 30(-39) m tall; bole often poorly shaped, sometimes sinuous, up to 60 cm in diameter, fluted at base or with small buttresses; bark surface finely fissured and flaky with irregular scales, pale brown to grey, inner bark fibrous, medium brown, with sticky, white latex; crown narrow, dense, lower branches drooping. Leaves arranged spirally, simple, entire, drooping, drip-tipped; petiole long, with 2 glands at apex; stipules caducous. Inflorescences axillary or terminal, crowded near twig tips, cymose with central flower female and remainder male. Flowers with 4-5 imbricate sepals; petals absent. Male flower with a lobed disk; stamens 10-20; pistillode rudimentary or absent. Female flower with a cupular disk; ovary superior, 2-4-locular with 1 ovule in each cell, styles 2-4, stigmas large. Fruit a large capsule with fleshy exocarp, usually splitting into 6 parts. Seed (pyrene) large, oblong, shiny. Seedling with epigeal germination; cotyledons emergent, fleshy; hypocotyl elongated; first 3-4 leaves in a whorl, subsequent ones arranged spirally.
In sample plots in Peninsular Malaysia the largest trees had attained 31 m in height and 42 cm in diameter after 36 years. The crown shows monopodial branching. The trees shed their leaves during the dry season, although defoliation twice a year is also reported; young leaves are strikingly bright pink. Flowers appear on the bare twigs, in Peninsular Malaysia in February-March and in July-August. It is unknown whether the same tree flowers twice a year. The flowers spread a musty fragrance, suggesting they are pollinated by insects. The fruits explode and thus scatter the seeds, but seeds are also dispersed by wild pigs and probably rodents feeding on the fruits.
Elateriospermum is the only genus within the tribe Elateriospermeae of the subfamily Crotonoideae. The "seed"" released from the fruit is actually a pyrene.

E. tapos is fairly common, in Peninsular Malaysia even common and gregarious. It occurs as an element of primary, evergreen or semi-evergreen, lowland and hill forest, up to 600 m altitude. It is found in well-drained localities on yellow loam, clay loam, yellow sandy clay, sandstone screes, shale or basalt.

E. tapos can be propagated by seeds, which show 40-70% germination in 14-42 days. The large seeds can be collected from underneath the trees. In Peninsular Malaysia E. tapos regenerates profusely in the shade, it grows up in small gaps and is strongly clumped. The trees coppice freely. In a survey of natural forest in Peninsular Malaysia an average of 0.83 trees/ha was found.

As E. tapos is common, it does not seem to be vulnerable to genetic erosion.

E. tapos seems a promising timber as it is available in sufficient quantities in Peninsular Malaysia and impregnation is easy. The apparently bad shape of the bole does, however, make it less attractive. Its coppicing capacity and fairly rapid growth are good for fuelwood production.

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F.M. Setyowati

Setyowati, F.M., 1998. Elateriospermum Blume. In: Sosef, M.S.M., Hong, L.T. and Prawirohatmodjo, S. (Editors): Plant Resources of South-East Asia No 5(3): Timber trees; Lesser-known timbers. PROSEA Foundation, Bogor, Indonesia. Database record: prota4u.org/prosea