Borneodendron (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Borneodendron Airy Shaw

Protologue: Kew Bull. 16: 359 (1963).

Family: Euphorbiaceae

Chromosome number: x= unknown; 2n= unknown

Vernacular names

• Malaysia: aara aara (Sabah), bangkau bangkau (Bajau, Sabah).

Origin and geographic distribution

Borneodendron is a monotypic genus found in Borneo (Sabah). The only species is B. aenigmaticum Airy Shaw.

Uses

The wood of B. aenigmaticum is used for local house construction and possibly for boat building. Because of its beautiful warm-brown colour, the wood may be suitable for attractive furniture and turnery articles.

Production and international trade

Utilization and supplies are very limited because B. aenigmaticum is only found on ultrabasic soils and often in protected forest areas.

Properties

B. aenigmaticum yields a medium-weight hardwood with a density of 795-885 kg/m³at 15% moisture content. Heartwood dark red-brown, sharply demarcated from the up to 8 cm wide yellow-brown sapwood; grain straight to shallowly interlocked; texture fine and even; planed surfaces slightly lustrous. Growth rings suggested by darker bands of tissue; vessels medium-sized, solitary and in radial multiples of 2-3, tyloses abundant; parenchyma abundant, apotracheal in narrow bands, distinct to the naked eye; rays fine, distinct to the naked eye on transverse surface; ripple marks absent; radial canals present, distinct with a hand lens.

Seasoning causes very little degrade. The wood is moderately hard. It can be planed to a very smooth surface, with but little picking up on radial faces. The wood is reputedly durable. Impregnation may be very difficult due to the abundance of tyloses. It is probably resistant to insect attack. Large trees are often hollow.

See also the table on microscopic wood anatomy.

Botany

A monoecious, large tree up to 50 m tall; bole up to 75 cm in diameter, occasionally with small buttresses up to 70 cm high; bark surface scaly, fissured, grey-brown, inner bark striate or mottled, pink-red; exudate watery and sticky at first, drying red. Indumentum on innovations of stellate scales. Leaves in whorls of 3, simple, entire, petiolate, obovate; stipules caducous. Male flowers in a terminal, subcapitate, nodding, catkin composed of 2-4, 3-flowered whorls; bracts large; sepals and petals absent; stamens 25-30, filaments connate into a column, anthers dorsally and apically pilose; disk absent. Female flower solitary, axillary, on a flattened, rigid pedicel; sepals 3, caducous; petals absent; ovary superior, 2-locular with 1 ovule per cell, stigmas bifid. Fruit a 2-locular, black, flattened capsule.

The tree has been found fruiting from January to September.

Ecology

B. aenigmaticum is locally abundant and may even form pure stands over limited areas on ultrabasic soils in primary forest and forest dominated by Gymnostoma sumatranum (Jungh. ex de Vriese) L.A.S. Johnson under xerophytic conditions, up to 1400 m altitude. It may also grow on other soils.

Genetic resources and breeding

B. aenigmaticum is a comparatively rare and endemic tree of ultrabasic soils. However, its occurrence in protected forest areas gives it some protection.

Prospects

Given its local occurrence, mainly in protected forest areas, no increase of the utilization of Borneodendron timber is to be expected. If ultrabasic soil is a prerequisite for this species, only small-scale silviculture may be expected at the most.

Literature

20, 23, 24, 28, 162, 1195.

P.C. van Welzen