Drypetes (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Drypetes Vahl

Protologue: Ecolog. amer. 3: 49 (1807).

Family: Euphorbiaceae

Chromosome number: x= 10;D. roxburghii:n= 20

Vernacular names

• Drypetes (En)
• Malaysia: arau (trade name), lidah-lidah (Peninsular), mentulang (Sabah)
• Philippines: tinaang-pantai (Filipino, trade name).

Origin and geographic distribution

Drypetes comprises about 200 species and is pantropical. About 10 species are found in the New World, some 60 in Africa and Madagascar, and the remainder in Asia and Australia. The genus is found throughout the Malesian region where some 60 species occur.

Uses

The exceptionally tough wood of Drypetes is used for general construction under cover (beams, joists, rafters, flooring), temporary construction, bridge and wharf superstructure, industrial flooring, furniture and cabinet making, rice mortars, tool handles, posts, piles, poles and railway sleepers. In the Philippines D. longifolia is considered useful for the manufacture of paper.

Production and international trade

Supplies are limited and Drypetes wood seldom reaches the market. In the Philippines the wood is traded in mixed consignments of medium-weight hardwood. In Sarawak it is sold as "arau", together with the wood of 2 other euphorbiaceous genera: Austrobuxus and Cephalomappa . In 1996 Papua New Guinea exported about 1220 m³of Drypetes logs at an average free-on-board (FOB) price of US$ 101/m³.

Properties

Drypetes yields a medium-weight to heavy hardwood with a density of (650-)740-1100 kg/m³at 15% moisture content. Heartwood pale yellow-brown occasionally mottled with dark or grey, not sharply demarcated from the paler sapwood; grain straight; texture very fine to moderately fine and even. Growth rings indistinct, boundaries marked by a narrow layer of dense, darker coloured tissue lacking parenchyma; vessels moderately small to medium-sized, mostly in radial multiples of 2-4, open; parenchyma abundant, apotracheal diffuse-in-aggregates forming a square mesh with the rays, distinct with a hand lens; rays moderately fine; ripple marks absent.

Shrinkage upon seasoning is high to very high. The wood stains readily and develops deep splits in the log when drying, but this problem does not occur when sawn fresh and stacked carefully. The wood is moderately hard to hard, strong and extremely tough. It is comparatively easy to work for a hard wood. The wood is durable under cover but perishable when in contact with the ground. The service life in a graveyard experiment in the Philippines was only 15 months. Impregnation of preservatives by pressure treatment is very good. The sapwood of D. lasiogynoides Pax & K. Hoffm. and probably D. longifolia occurring in Papua New Guinea is reported non-susceptible to Lyctus , but that of D. microphylla susceptible.

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

Botany

Generally evergreen, dioecious, small to medium-sized trees up to 30(-40) m tall; bole straight to somewhat sinuous in smaller trees, branchless for up to 20 m, up to 60(-80) cm in diameter, sometimes fluted or with short buttresses; bark surface smooth to finely fissured, often rugose or lenticellate, grey to grey-green, inner bark fibrous to granular, yellowish or pale brown to orange-brown or mottled orange-brown and fawn; crown usually dense, often rather small. Leaves arranged spirally, simple, entire or dentate, often unequal at base; stipules persistent or caducous. Flowers in an axillary or cauliflorous fascicle; sepals 4-5, imbricate, deciduous in fruit; petals absent. Male flowers with few to many, free stamens; disk annular or sinuate; pistillode small to obsolete. Female flower with an annular disk; ovary superior, 1-3-locular with 2 ovules in each cell, styles 1-3, very short, stigmas broad. Fruit drupaceous, leathery or fleshy, with 1-3 seeds each contained in an often thin stone (pyrene). Seedling with epigeal germination; cotyledons emergent, leafy; hypocotyl elongated; leaves alternate, involute.

In Java most Drypetes species can be observed flowering in August and September.

Drypetes forms a "bridge" between the Euphorbiaceae and the Flacourtiaceae . There is little support for the suggestion that it should be placed in the latter family.

Ecology

Drypetes is found scattered in primary lowland, evergreen rain forest, occasionally in monsoon forest, or in montane forest, up to 1700 m altitude. D. longifolia ascends up to 4000 m on Mount Kinabalu (Sabah). Most species occur in well-drained habitats on sandy to sandy loam soils, occasionally on clay or limestone, or in periodically flooded locations. D. littoralis is found on sandy beaches but also in inland hill forest. D. sibuyanensis is usually found in swamp forest or kerangas.

Silviculture Drypetes can be propagated by seed. Pyrenes of D. kikir sown with adhering pulp germinated for about 25% in one seed lot and about 95% in another in 1-3.5 months. Pyrenes of D. longifolia with adhering pulp germinated for about 90% in 42-89 days, whereas those of D. pendula germinated for about 30% in 24-68 days. D. longifolia is known to form root suckers.

Genetic resources and breeding

Comparatively many Drypetes species are narrow endemics and therefore liable to genetic erosion or extinction through destruction of their habitat.

Prospects

The extremely tough wood of Drypetes makes it very suitable for the handles of striking tools and is therefore likely to be increasingly utilized.

Literature

26, 28, 32, 33, 34, 36, 70, 125, 162, 163, 209, 235, 238, 267, 300, 301, 348, 436, 464, 525, 543, 553, 780, 829, 831, 861, 934, 955, 974, 1038, 1195, 1221, 1242.