Petersianthus (PROSEA)
Introduction |
Petersianthus Merr.
- Protologue: Phil. Journ. Sci., Bot. 11: 200 (1916).
- Family: Lecythidaceae
- Chromosome number: x= unknown; 2n= unknown
Vernacular names
- Philippine rosewood (En, trade name)
- Philippines: toog (Filipino), kapullan (Cebu Bisaya), magtalisai (Samar-Leyte Bisaya).
Origin and geographic distribution
Petersianthus comprises only 2 species. One occurs in tropical West Africa. The second species, P. quadrialatus (Merr.) Merr. (synonym: Combretodendron quadrialatum (Merr.) Knuth), is endemic to the Philippines.
Uses
The wood of P. quadrialatus is mainly used for the production of face veneer and fancy plywood, and for the production of pulp and paper. It is also suitable for general construction (beams, joists), panelling, bridge building, mine timber, pallets and the production of charcoal. It is potentially useful for poles and piles, and vehicle bodies.
The seeds are reported edible and taste like groundnut. The leaves have been used medicinally against rash.
Production and international trade
Utilization of P. quadrialatus wood gained much importance after the proper method of handling was developed in the 1970s. Fairly large supplies were available, especially in Mindanao, Samar and Leyte, but these have diminished rapidly. Small amounts may have reached the international market, but there are no statistics available on the local consumption nor on export.
Properties
P. quadrialatus yields a medium-weight hardwood with a density of 615-720 kg/m3at 15% moisture content. Heartwood pale red turning reddish-brown with pale streaks upon exposure, sharply demarcated from the pale and fairly wide sapwood; grain interlocked; texture moderately fine to moderately coarse. Growth rings indistinct, when visible indicated by somewhat denser latewood; vessels moderately small to moderately large, predominantly solitary and in radial multiples of 2-3, tyloses rare, occasional chalky white deposits; parenchyma paratracheal vasicentric to aliform and confluent, apotracheal in narrow bands spanning up to 10 rays, sometimes appearing as irregular bands, variable in width and occurrence, visible only with a hand lens; rays very fine to moderately broad, indistinct to the naked eye; ripple marks absent.
Shrinkage is rather high and the wood is rather difficult to season, as it is likely to warp and split. It is hard, moderately strong and tough, moderately hard to work, but can be finished satisfactorily. The wood is durable for interior use and slightly durable when exposed to the weather or in contact with the ground; in a graveyard test in the Philippines it lasted for about 17 months. The heartwood is amenable to preservative treatment. The heartwood is susceptible to dry-wood termites and the sapwood is susceptible to Lyctus .
The average fibre length is 2.4 mm.
See also the tables on microscopic wood anatomy and wood properties.
Botany
A deciduous, medium-sized to fairly large tree up to 40 m tall; bole straight, cylindrical, branchless for up to 20(-30) m, up to 100(-250) cm in diameter, occasionally with buttresses up to 2 m high; bark surface flaky to deeply fissured, dark brown to greyish-red, inner bark tough and fibrous, pinkish; slash with a strong foetid smell. Leaves arranged spirally, simple, obscurely toothed, abruptly acuminate; stipules early caducous. Flowers in axillary and terminal panicles forming a corymb; calyx 4-lobed, the tube 4-angled or 4-winged; petals 4, free, white; stamens numerous, forming a small tube at base; disk present; ovary inferior, 4-locular with many ovules in 2 rows in each cell, style 1, slender. Fruit a 1-4-seeded capsule, indehiscent, almost circular in outline, with 4 large, papery wings, the seed-bearing portion very narrow. Seedling with epigeal germination; cotyledons emergent, leafy; hypocotyl elongated; first pair of leaves opposite, subsequent ones arranged spirally.
Early development in the nursery is rapid and height increment in the first 4 months averages 31 cm. Height increment in a 2-year-old plantation was 0.7-2.9 m and diameter increment 0.6-3.8 cm. Flowering is erratic and apparently triggered by sudden fluctuations in temperature. However, flowering is usually observed between July and February. The fruits take about 1 month to mature and mature fruits are generally present between March and May. Trees remain leafless during flowering and fruiting and buds appear after seedfall. Seed is dispersed by wind or animals.
The strange disjunct distribution of Petersianthus remains unexplained. The generic name Combretodendron is sometimes encountered in literature. It is not validly published and has been replaced by Petersianthus .
Ecology
P. quadrialatus is fairly common and grows scattered though locally common in primary rain forest at low to medium altitudes, on well-drained soils near river banks or on hill sides.
Silviculture P. quadrialatus can easily be propagated by seed. Seed loses its viability very rapidly and hence it should be sown immediately after collection. After storing for 13 days the germination rate is about 60%. From the Philippines it is reported that when establishing plantations the young plants must be ring weeded. A mortality of about 11% was recorded for non-weeded control plots. Natural regeneration is very scarce. It has been suggested that various animals (e.g. insects, rodents, birds) feed on the seed up in the tree so that very few seeds reach the forest floor. Seedlings are found as far as 200 m from mother trees, especially between buttresses or in soil that has accumulated in depressions. Seedlings establish easiest on bare soil, e.g. along roads. P. quadrialatus coppices easily, at least when young. Until the 1970s the tree was left unexploited and could be seen towering in logged-over forest.
Genetic resources and breeding
The high demand in the last 20 years has led to stands of P. quadrialatus being depleted drastically. So it has become vulnerable to genetic erosion and is considered a vanishing timber. Plantation establishment, however, may still secure its genetic potential to a large extent.
Prospects
If plantations of P. quadrialatus can be established successfully, its utilization will probably increase.
Literature
87, 154, 228, 234, 235, 464, 489, 530, 575, 665, 666, 702, 780, 784, 785, 803, 804, 894, 934, 955, 959, 960, 974, 1086, 1171.
D.S. Alonzo