Aporosa (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Aporosa Blume

Protologue: Bijdr. fl. Ned. Ind. 10: 514 (1825).

Family: Euphorbiaceae

Chromosome number: x= unknown;A. dioica:n= 26

Vernacular names

• Indonesia: sasah (Sundanese)
• Malaysia: sebasah (Peninsular)
• Philippines: malabignai
• Thailand: mueat
• Vietnam: ngãm, thầu táu.

Origin and geographic distribution

Aporosa comprises about 80 species occurring in Sri Lanka and India to Indo-China, southern China, Thailand, throughout the Malesian region (except for the Lesser Sunda Islands) towards the Solomon Islands. Within Malesia some 60 species are present which are distributed as follows: 27 in Peninsular Malaysia, 17 in Sumatra, 6 in Java, 32 in Borneo, 3 in Sulawesi, 5 in the Moluccas, 9 in the Philippines, 22 in New Guinea.

Uses

The wood of Aporosa has been used for local house construction (rafters, flooring etc.), furniture, and small household implements like tool handles and rice pounders. It is suitable for firewood.

The bark and sometimes also the leaves of A. frutescens used to be used in the batik industry as a mordant to fix the red dye from Morinda citrifolia L. The fruit of A. prainiana is reported to be edible.

Production and international trade

As the supply is generally small, the wood of Aporosa is utilized on a local scale only.

Properties

Aporosa yields a medium-weight hardwood with a density of 570-890 kg/m³at 15% moisture content. Heartwood pale yellow-brown to brown with orange or purple-red tinges, not sharply differentiated from the sapwood; grain straight; texture moderately fine and uneven; wood with appreciable silver grain on quarter-sawn surfaces. Growth rings absent; vessels moderately small to medium-sized, often distinctly angular, solitary in some species but mostly in radial multiples of 2-4, tyloses sparse; parenchyma abundant, apotracheal diffuse-in-aggregates, visible only with a hand lens; rays of 2 sizes, very fine and medium-sized to moderately broad; ripple marks absent.

The wood is moderately hard and strong and is probably easy to work, as it is non-siliceous. It is moderately durable when exposed to the weather or in contact with the ground.

The average fibre length of A. dioica is 1.630 mm. Leaves accumulate aluminium, rendering them pale when dried.

See also the table on microscopic wood anatomy.

Botany

• Evergreen, dioecious, small to medium-sized trees up to 30(-50) m tall; bole usually straight, up to 60 cm in diameter, without buttresses; bark surface smooth to finely scaly or finely fissured, often powdery, inner bark firmly fibrous and dark red-brown or granular and orange-brown.
• Leaves arranged spirally, simple, entire to toothed, often finely dotted below; petiole usually kneed; stipules caducous or persistent.
• Flowers small, apetalous; disk absent. Male flowers in solitary or clustered, axillary catkins; sepals 3-4; stamens 2(-5); pistillode minute. Female flowers in a shorter and fewer-flowered spike or cluster, rarely in a more extended raceme; sepals 3-6; ovary superior, 2(-4)-locular with 2 ovules in each cell, styles bifid, persistent.
• Fruit a few-seeded capsule, splitting regularly or irregularly or not dehiscent, ovoid to globose, with a leathery-fleshy wall.
• Seed with a dry or fleshy seed-coat.
• Seedling with epigeal germination; cotyledons emergent, leafy, bilobed; hypocotyl elongated; all leaves arranged spirally.

The flowering-to-fruiting period of A. nigricans in Pennsular Malaysia is about 12 weeks.

Although Aporosa may be quite abundant in some forests, the trees are often overlooked as they show no striking features. Aporosa belongs to the subfamily Phyllanthoideae and the tribe Antidesmeae . The generic name is often spelled as Aporusa ; the present spelling, Aporosa, is clearly correct, according to the International Code of Botanical Nomenclature.

Ecology

Aporosa is locally common and is usually found in the understorey of primary and secondary lowland rain forest, both in well-drained locations and in seasonal or permanent swamp forest. Individual species can be encountered in more disturbed or more open sites, e.g. in mixed bamboo forest and in montane localities, in New Guinea often in fagaceous forest, up to 2000 m altitude.

Silviculture

Aporosa can be propagated by seed. Seeds sown with adhering pulp generally germinate well (80-98%). Germination was very poor, however, for A. microstachya (6%), A. prainiana (14-25%) and A. stellifera (12%). Germination usually starts 2-3 weeks after sowing and is completed within 2 months. Most species are reported to be fire-resistant.

Genetic resources and breeding

There is little risk of genetic erosion in Aporosa, since at present it is rarely felled for timber.

Prospects

As Aporosa is a fairly common forest component in South-East Asia, its wood might become increasingly important.

Literature

22, 26, 28, 32, 33, 34, 36, 70, 162, 163, 174, 189, 209, 267, 436, 543, 553, 696, 800, 829, 831, 834, 835, 861, 883, 908, 974, 996, 1038, 1195, 1221.