Pterygota (PROSEA)
Introduction |
Pterygota Schott & Endl.
- Protologue: Melet. Bot.: 32 (1832).
- Family: Sterculiaceae
- Chromosome number: x= unknown;P. alata: 2n= 40,P. macrocarpaK. Schumann: 2n= 36
Vernacular names
- Mabin, pterygota (trade name)
- Malaysia: kasah (Peninsular), melebu (Iban, Sarawak)
- Papua New Guinea: white tulip oak (En).
Origin and geographic distribution
Pterygota comprises about 20 species occurring throughout the tropics. In Asia they are found from Bangladesh (Chittagong) to Indo-China, Thailand, throughout the Malesian region (except for Sumatra), the Solomon Islands and northern Australia.
Uses
When treated, the wood of Pterygota is suitable for general construction, bridge and wharf superstructure, railway sleepers and poles. It is used for flooring, interior finish, furniture and cabinet work, joinery, mouldings, panelling, cladding, lining, steps, hand rails, tool handles, pattern work, packing boxes, pallets, carvings, shoe heels, toys and novelties and turnery. It is often applied as face veneer and for concrete shuttering. It is also suitable for manufacture of cement-bonded wood-wool board and may be suitable for producing short fibre pulp.
Production and international trade
Supplies of Pterygota are generally limited and the wood is mainly used locally, but small amounts are imported into Japan from Papua New Guinea and the Solomon Islands. In 1996 the export from Papua New Guinea amounted to 7800 m3of round logs at an average free-on-board (FOB) price of US$ 98/m3.
Properties
Pterygota yields a medium-weight to heavy hardwood with a density of 460-980 kg/m3at 15% moisture content. Heartwood pale yellow-white to pale brown, not clearly differentiated from the pale yellow to straw sapwood; grain straight or shallowly interlocked; texture medium to coarse and uneven; wood with silver grain and characteristic ray pattern on radial surface; fresh wood with offensive smell. Growth rings indistinct, occasionally indicated by zones with fewer, or wavier parenchyma bands; vessels moderately large, solitary and in radial multiples of 2-4(-more), occasionally in clusters, tyloses rare, but gummy deposits occasionally present; parenchyma moderately abundant to abundant, scanty paratracheal, vasicentric, or apotracheal in broad, continuous or interrupted bands; rays medium-sized to moderately broad with occasional very wide rays; fine ripple marks present due to storied arrangement of parenchyma cells.
Shrinkage of the wood when seasoned is moderate to high. During preliminary air drying short surface checks usually develop, which extend during kiln drying. It takes about 5 days to kiln dry boards 25 mm thick from the green condition. Quarter-sawn boards develop some end checks whereas back-sawn boards may show severe surface checking. The wood is soft to moderately hard and may be slightly heavier and harder in the periphery of the stem. It is moderately strong, tough and very shock resistant. The wood is fairly easy to saw, plane and finish, but has a tendency to tear when quarter-sawing boards with interlocked grain. A sticky substance is released when sawing green stock, so the saw blades have to be cleaned frequently. Stock may be sliced, but peeling P. horsfieldii may not be satisfactory due to the presence of harder and softer zones. The wood is moderately durable. The sapwood of P. horsfieldii is susceptible to Lyctus . The sapwood and heartwood are permeable when treated with preservatives under pressure. Logs are very susceptible to blue stain, termites and pinhole borer attack unless rapidly removed from the forest and treated with appropriate prophylactic preservatives.
See also the tables on microscopic wood anatomy and wood properties.
Botany
Deciduous, monoecious, medium-sized to large trees up to 50 m tall; bole cylindrical to tapering, up to 120 cm in diameter and branchless for up to 36 m, with thin, small to tall buttresses; bark surface smooth to shallowly fissured, mauve-grey, inner bark pale brown; crown dense, dark. Twigs slender, prominently wrinkled. Leaves arranged spirally, simple, entire, palmately veined; stipules subulate, caducous; petiole kneed. Flowers in a short, terminal or subterminal panicle or raceme, unisexual; sepals 5, almost free; petals absent. Male flower with 8-10 or 20-25 sessile anthers placed on a staminal tube and a rudimentary ovary. Female flower with staminodes; ovary superior, with 3-5 partly fused carpels each with many ovules, styles short. Fruit a stalked, globose, woody, many-seeded follicle, splitting on one side. Seeds with a large wing on one side. Seedling with epigeal germination; cotyledons emergent, leafy; hypocotyl elongated; leaves alternate-spiral from the outset (occasionally the first 2 opposite in extra-Malesian species).
In trials in West and East Java with P. alata at 19-31 years of age, the mean annual increment was 0.9-1.9 cm in diameter and 0.8-1.1 m in height. Branches are produced in pseudowhorls and their tips curve upwards in a Terminalia -like fashion. In Peninsular Malaysia P. horsfieldii has been observed to flower and fruit in mast fruiting years. In Thailand P. alata flowers and fruits in December-March. The winged seeds are dispersed by wind.
Ecology
Pterygota is found scattered or rarely gregarious in primary, lowland rain forest, up to 1000 m altitude, in areas with a short but pronounced dry period. It occurs on fertile soils and apparently tolerates periodic droughts. P. alata prefers flat alluvial soils and periodically inundated localities. In Papua New Guinea P. horsfieldii is locally common in monsoon forest.
Silviculture Pterygota can be propagated by seed. For P. alata there are about 1250 seeds without wings per kg. Seeds should be sown in the shade and those of P. alata have 80-85% germination in 7-203 days. In a trial in West Java P. alata regenerated naturally with an average of 19 seedlings/m2.
Genetic resources and breeding
Pterygota is widespread but rare and occurs only locally, so is at serious risk of genetic erosion from habitat destruction.
Prospects
The wood of Pterygota is of reasonable quality and may have potential for face veneer and as pulp for paper.
Literature
40, 61, 80, 125, 209, 267, 300, 304, 348, 360, 378, 455, 464, 487, 536, 600, 678, 758, 829, 831, 888, 933, 1023, 1038, 1145, 1169, 1221, 1242.