Trewia (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Trewia L.

Protologue: Sp. pl. 2: 1193 (1753); Gen. pl., ed. 5: 500 (1754).

Family: Euphorbiaceae

Chromosome number: x= 11;T. nudiflora: 2n= 22

Vernacular names

• Indonesia: bebeka burilang (Lampung, Sumatra), gemblok (Javanese), kayu tanah (Sumatra). Burma (Myanmar): setkadon
• Laos: pop, pop¹
• Thailand: ma fo (general), ma pop (northern)
• Vietnam: lươu bươu.

Origin and geographic distribution

Trewia is a monotypic genus occurring in India, Sri Lanka, Burma (Myanmar), Indo-China, southern China, Thailand, Peninsular Malaysia, Sumatra, Java, Borneo (Kalimantan) and the Philippines. The only species is T. nudiflora L. (synonyms: Mallotus cardiophyllus Merr., T. macrophylla Roth, T. macrostachya Klotzsch).

Uses

The wood of T. nudiflora is used for light construction, household implements, matches, packing cases and for rotary veneer. In India it is used for drums and carving.

T. nudiflora contains nudiflorine, a pyridone alkaloid with insecticidal properties and trewiasine, a mytansinoid compound possessing significant cytotoxic activity against various human cancer cell lines in vitro. The seed yields an oil.

Production and international trade

As the available supplies are small, the use of T. nudiflora wood is very limited and on a local scale only.

Properties

T. nudiflora yields a lightweight hardwood with a density of 360-465 kg/m³at 15% moisture content. Heartwood white, turning pale brownish-grey upon exposure, not clearly demarcated from the sapwood; grain straight; texture moderately fine and even. Growth rings distinct or lacking; vessels moderately small to moderately large, solitary and in radial multiples of 2-3(-5), open, tyloses rare; parenchyma abundant, paratracheal vasicentric, apotracheal parenchyma diffuse to diffuse-in-aggregates and in narrow bands; rays fine, visible with a hand lens; ripple marks absent.

The wood seasons without degrade, but with high risk of discolouration due to blue stain; therefore it needs to be sawn when green. The wood is soft and weak. It is easy to saw and work to a smooth finish. It is non-durable.

See also the table on microscopic wood anatomy.

Botany

A deciduous, dioecious, medium-sized to fairly large or rarely large tree up to 35(-45) m tall; bole fairly straight and cylindrical, up to 80(-200) cm in diameter, without buttresses; bark surface greyish; crown irregular, thin. Twigs grey, turning brown with age. Indumentum of stellate or clustered hairs. Leaves decussate, simple, entire, palmately veined with 3-5 main veins, usually densely hairy below; petioles often unequal; stipules small, caducous. Flowers unisexual; petals absent; disk absent. Male flowers in axillary, few-flowered cymes aggregated into a raceme, about 10 mm across; calyx 5-lobed; stamens numerous; pistillode absent. Female flowers in a lax, axillary, 1-4-flowered raceme; calyx rupturing irregularly; ovary superior, 2-4-locular with 1 ovule in each cell, styles short, stigmas elongated, recurved and plumose. Fruit a leathery drupe. Seedling with epigeal germination; cotyledons emergent; hypocotyl elongated; leaves arranged spirally at first, later on decussate.

Early growth of seedlings is slow and they attain only 13-25 cm after the first year. Later on growth is rapid with a mean height of 2.7 m and a mean diameter of 8.0 cm when 4 years old. Indian wood samples showed an annual diameter increment of 0.7-1.7 cm. Flowers appear before or together with the new leaves. In Java T. nudiflora has been observed flowering in June-December. The fruits are eaten by mammals like rhinoceros and deer. Seeds eaten by rhinoceros and defecated into grassland latrines developed into robust seedlings. Fruits are buoyant and are also dispersed by streams and rivers.

Trewia closely resembles Mallotus , but differs in its large male flowers, few-flowered female inflorescences, strongly elongated stigmas and drupaceous fruit.

Ecology

T. nudiflora is found very locally and scattered in primary and secondary forest, up to 450(-1200) m altitude. It occurs most frequently near rivers and streams, but also on low ridges, on loams or loamy soils with coral limestone.

Silviculture T. nudiflora can be propagated by seed and has 4200-8100 seeds/kg. The seed can be extracted after fruits have been spread out in the sun for several days to soften. Seed viability decreases when seed is stored in airtight containers. In India soaking seed in water for up to 48 hours accelerates germination. Germination of fresh seeds attains 70-80% and starts after 10-14 days. Seedlings raised in the nursery should be copiously watered during dry weather as they are sensitive to drought. Weeding after planting is important. Plants are easily suppressed by more vigorous plants, although side shade is beneficial in the early stages to prevent damage from drought. T. nudiflora coppices vigorously and produces root suckers.

Genetic resources and breeding

Given the wide geographical distribution of T. nudiflora , there is no immediate danger of genetic erosion.

Prospects

The very limited supplies together with the poor wood properties make it unlikely that T. nudiflora wood will increase in importance.

Literature

17, 26, 28, 33, 34, 70, 174, 238, 364, 436, 697, 736, 834, 874, 883, 974, 1038, 1104, 1169, 1195, 1221, 1226.

Nguyen Nghia Thin