Scorodocarpus (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Scorodocarpus Becc.

Protologue: Nuovo Giorn. Bot. Ital. 9: 274 (1877).

Family: Olacaceae

Chromosome number: x= unknown; 2n= unknown

Vernacular names

• Kulim (trade name). Bawang hutan (Am, En).
• Brunei: bawang hutan
• Indonesia: kayu bawang (Sumatra, Kalimantan), kayu bawang utan (Kalimantan), selaru (Kalimantan)
• Malaysia: bawang hutan (Sabah, Sarawak), sagan berauh, ungsunah (Sarawak)
• Thailand: krathiam ton, kuleng, kulim (peninsular).

Origin and geographic distribution

Scorodocarpus is a monotypic genus occurring in peninsular Thailand, Peninsular Malaysia, Sumatra and Borneo. The only species is S. borneensis (Baillon) Becc. (synonym: Ximenia borneensis Baillon).

Uses

The wood of Scorodocarpus is used for medium to heavy construction under cover (beams, joists, posts, door and window frames, flooring, rafters), bridge building, salt-water piling (with bark on), boat keels, mine props, transmission posts, agricultural implements and sleepers in temporary railway lines.

In Sarawak the young leaves are eaten as a vegetable. The fruit is edible and is sometimes used as a substitute for garlic. The fruits and also an infusion of the bark are sometimes used as an antidote for "antiaris" ( Antiaris toxicaria Lesch.) poisoning. An extract from the fruits shows antimicrobial activity.

Production and international trade

Because of the limited supplies and local occurrence, Scorodocarpus wood is harvested and traded mainly locally, and only when no alternatives are available. It is occasionally found in mixed consignments of medium-weight hardwood.

Properties

S. borneensis yields a medium-weight to heavy hardwood with a density of 645-1080 kg/m³at 15% moisture content. Heartwood reddish-brown to dark purplish-brown towards the centre, clearly demarcated from the up to 5 cm wide, white or pale yellow sapwood; grain shallowly or deeply interlocked, sometimes straight, wavy or irregular; texture moderately fine to moderately coarse and even; wood with silver fleck (vessel lines) on longitudinal surfaces and with strong odour of garlic when fresh and a peppery smell when dry. Growth rings indistinct; vessels moderately small to medium-sized, solitary but more often in radial multiples of 2-3(-6), tyloses mostly well-developed, occasionally with white deposits; parenchyma moderately abundant, apotracheal diffuse and diffuse-in-aggregates; rays very fine to moderately fine, visible with a hand lens; ripple marks absent.

Shrinkage upon air seasoning is low to high, especially tangentially, and the wood seasons fairly rapidly with moderate splitting and slight end-checks as the main source of degrade. Boards 13 mm and 38 mm thick take about 2 and 4 months, respectively, to air dry. It takes about 8 days at a temperature of 55-70C and an initial relative humidity of 85% to kiln dry 25 mm thick boards to 14% moisture content. The wood is moderately hard to hard and very strong, but the core is often defective. The wood is moderately easy to saw and the finish after planing depends on the degree of interlocked grain present in the material. Turning properties are variable; boring, mortising and sanding gives good results but shaping is fairly poor. Due to its hardness it is difficult to peel. Nailing properties are rated as very poor. The wood is moderately durable to durable; the average service life of test stakes in a graveyard test in Peninsular Malaysia was about 4 years. The absorption of a mixture of creosote and diesel oil when using the open tank method is about 110 kg/m³. The wood is susceptible to pinhole borers and longhorn beetles, moderately resistant to fungal attack and susceptible to dry-wood termites. The sapwood is non-susceptible to Lyctus .

The average fibre length is 2.151 mm. The volatile, antimicrobial compound from the fruits has been identified as methyl-methylthiomethyl-disulfide.

See also the tables on microscopic wood anatomy and wood properties.

Botany

• An evergreen, medium-sized to large tree up to 40(-60) m tall, all parts smelling of garlic; bole columnar, branchless for up to 25 m, up to 80(-150) cm in diameter, often piped, occasionally with small buttresses; bark surface shallowly fissured and flaking into thin rectangles, grey-brown to dark red-brown, inner bark fibrous, purplish-red, inwards with orange flecks.
• Leaves arranged spirally, simple, entire, exstipulate; petiole swollen distally.
• Flowers in an axillary, short raceme, 4-5-merous; calyx cup-shaped, margin wavy to toothed; petals reflexed, white, hairy inside; stamens 8 or 10, inserted in pairs about halfway on the petal; ovary superior, imperfectly 3-4-locular with a single ovule in each cell, stigma minutely lobed.
• Fruit a thinly fleshy, subglobular, 1-seeded, green drupe; endocarp woody with vertical strands.
• Seedling with hypogeal germination; cotyledons not emergent; hypocotyl not developed; epicotyl with a few scale leaves followed by normal, spirally arranged leaves.

Sapling leaves are alternate-distichous on the branches but arranged spirally on the orthotropic leader. Growth is slow and trees in a large sample in natural forest in Peninsular Malaysia showed an average annual diameter increment of 0.2-0.3 cm. In plantation trials in Peninsular Malaysia the largest trees of 30-33 years old measured 18-29 cm in diameter and 18-21 m in height. In Peninsular Malaysia flowering is in January-July and fruiting more or less throughout the year; in Borneo fruiting is usually in June-September.

Ecology

S. borneensis occurs scattered but may be locally common or even gregarious in primary rain forest, up to 600(-900) m altitude.

Silviculture

S. borneensis can be propagated by seed or by wildlings. Before storage seeds should be sun-dried for about 10 days. There are about 27 000 dry pyrenes/kg and they show about 70% germination in 11-32 months, fruits have about 40% germination in 9-16 months. Stumps may coppice easily. For optimal growth it requires well-drained soils. The mean timber volume of S. borneensis found in a survey of 20 000 ha of the Semangus forest, Sumatra is about 0.5 m³/ha.

Genetic resources and breeding

There are no records of S. borneensis in germplasm collections or seed banks. As it has a wide geographical distribution it is not at risk of genetic erosion.

Prospects

It is unlikely that the use of the timber of S. borneensis will increase in the near future. It has no potential for reforestation.

Literature

3, 50, 112, 151, 162, 163, 193, 198, 218, 259, 261, 267, 341, 354, 436, 464, 536, 553, 571, 677, 678, 740, 741, 757, 829, 831, 832, 861, 933, 1023, 1038, 1040, 1048, 1052, 1221, 1242.

L.S.L. Chua