Excoecaria (PROSEA Timbers)

Plant Resources of South-East Asia Introduction

List of species

Excoecaria L.

Protologue: Syst. nat., ed. 10, 2: 1288 (1759).

Family: Euphorbiaceae

Chromosome number: x= unknown; E. agallocha: 2n= c. 70, 140, 168, E. cochinchinensisLour.: 2n= 22, E. indica:n= 32

Vernacular names

• Ludai (trade name). Milky mangrove (En)
• Indonesia: bintaos laut (Sundanese), menengan (Bali), penggung (Java)
• Malaysia: ludai (general), bebuta (Peninsular), buta-buta (Sabah, Sarawak)
• Philippines: buta-buta (Filipino)
• Thailand: tatum
• Vietnam: gia.

Origin and geographic distribution

Excoecaria comprises about 40 species occurring in tropical Africa, Madagascar, and from India and Sri Lanka east to Indo-China, southern China, Taiwan, the Ryukyu Islands, Thailand, throughout the Malesian region, northern Australia and the Pacific islands. Most species are found in the Asiatic tropics; 12 in Malesia.

Uses

The wood of Excoecaria is weak and used for utility furniture, interior finish, mouldings, canoes, packing cases, clog soles, toys, and matches. It is suitable for light construction when properly treated. It yields a good quality charcoal and is frequently used for firewood, although the wood of some species gives off an unpleasant and irritating smoke. It yields good raw material for the production of kraft pulp. The wood of E. indica has been used as core veneer.

Trees of E. agallocha growing along the coast may form pieces of resinous, aromatic wood called "garu laut" or "garu mata buta" on Ternate and "menengan" on Bali. It serves as a substitute for "gaharu" (incense) from Aquilaria spp. An oil obtained from this wood is applied medicinally against sores, eczema and scabies. The leaves of E. agallocha and E. indica contain tannin and are used to prepare a dye. The bark of the former and young fruits of the latter are used as fish poison but seeds of E. indica are edible. The bark of E. agallocha is also used as an ingredient for dart poison and as a purgative. Its leaves are poisonous to cattle.

Production and international trade

Excoecaria wood is rarely used for timber, mainly due to its toxic sap. In 1996 Papua New Guinea exported only 3 m³of "milky mangrove" logs at an average free-on-board (FOB) price of US$ 100/m³.

Properties

Excoecaria yields a lightweight to medium-weight hardwood with a density of 340-780 kg/m³at 15% moisture content. Heartwood pink-white to pale brown or pale yellow-brown, not clearly differentiated from the straw-coloured sapwood; grain straight or interlocked; texture moderately fine and even. Growth rings usually visible; vessels very small to medium-sized, in radial multiples of 2-4 sometimes over 4, tyloses rare or absent; parenchyma abundant, apotracheal in narrow, closely spaced bands, visible with a hand lens; rays very fine; ripple marks absent.

Shrinkage upon seasoning is moderate. The wood is soft to moderately hard and weak. It is easy to work and carve. The wood is non-durable and susceptible to sap-stain fungi, dry-wood termites and ambrosia beetles. The sapwood is susceptible to Lyctus .

The average fibre length of E. agallocha is 1.07 mm. The abundant white latex in bark and fruits blisters human skin and causes blindness in contact with the eyes.

See also the table on microscopic wood anatomy.

Botany

• Evergreen or briefly deciduous, usually dioecious, small to medium-sized trees up to 25(-40) m tall, occasionally shrubs; bole cylindrical, sometimes poorly shaped, up to 60(-100) cm in diameter, without buttresses; bark surface smooth to finely fissured or with lenticels frequently joining up to form vertical or diagonal stripes, grey-brown, inner bark pinkish, exuding abundant dirty white to pale yellow latex.
• Leaves arranged spirally or opposite, simple, entire or crenulate, shortly petioled, with two glands at the base of the blade; stipules small.
• Flowers unisexual, small, in an axillary or terminal, unisexual or androgynous raceme or spike; bracts small, biglandular; sepals (2-)3, free or shortly connate; petals absent; disk absent. Male flowers 1-3 together; stamens (2-)3; pistillode absent. Female flowers at the base of the raceme or on separate inflorescences; ovary superior, 3-locular with 1 ovule in each cell, styles simple, connate at base, recurved.
• Fruit a small, smooth, green to dark brown, dehiscing capsule with 3 bivalved parts.
• Seed without caruncle.
• Seedling with epigeal germination; cotyledons emergent; hypocotyl elongated; all leaves arranged spirally, conduplicate.

In Bangladesh the mean annual diameter increment of E. agallocha in different plots in mangrove forest ranged from 0.05-0.18 cm. Young leaves are pink. Old trees of E. indica have branches drooping to the ground. The seeds are probably dispersed by water.

E. parvifolia Müll. Arg. seems to be a promising timber species of northern Australia.

Ecology

E. agallocha is frequently found in the drier parts of mangrove swamps and along rocky shores, and may occur in pure stands. The other species occur in primary or occasionally secondary, evergreen rain forest, up to 800 m altitude. E. indica is additionally found in sago swamps, gallery forest and on the inland edge of mangrove swamps.

Silviculture Excoecaria can be propagated by seed. Sown fruits of E. indica have only 5% germination in 318-413 days. In India direct sowing by broadcasting the viable seeds of E. agallocha has proven very satisfactory. The species has become more common in Indian mangrove forest because the trees coppice well and can survive repeated felling. Special precautions must be taken when logging Excoecaria trees, because of their aggressive latex. In North Sumatra and Peninsular Malaysia localized mass defoliation of E. agallocha by caterpillars of the noctuid Achaea janata has been observed, but trees survived the attack.

Genetic resources and breeding

Apart from a few individuals in botanical gardens, there are no records of ex situ conservation of Excoecaria species. E. myrioneura and E. virgata are rare.

Prospects

As Excoecaria wood is of inferior quality, its future use will probably be limited to the production of pulp and charcoal.

Literature

26, 28, 32, 33, 34, 36, 70, 151, 162, 163, 209, 238, 267, 300, 348, 436, 464, 696, 717, 829, 831, 853, 861, 974, 1038, 1195, 1218, 1221, 1232, 1242.