6134

5(3): Timber trees; Lesser-known timbers

Potoxylon Kosterm.

Mal. Nat. Journ. 32: 143 (1978).

LAURACEAE

x = probably 12 as in most other Lauraceae genera; 2n = unknown

Malagangai (trade name). Brunei: legangai (Dusun), tebellian kebuau (Iban). Malaysia: belian kapok, belian kebuau (Iban, Sarawak), belian malagangai (Dayak, Sarawak).

Potoxylon is a monotypic genus endemic to Borneo (all parts). The only species is P. melagangai (Sym.) Kosterm. (synonym: Eusideroxylon melagangai Sym.).

The wood of P. melagangai is used for heavy construction, boat building, posts, paddles, fences, pepper posts and shingles. It is a popular substitute for the more durable "ulin"" (Eusideroxylon zwageri Teijsm. & Binnend.) especially in areas where the latter is not readily available.

As the supplies are only limited, P. melagangai timber is seldom traded commercially. In areas where it is comparatively common, it may be traded on a local scale, or occasionally exported in mixed consignments with "ulin"". In Sarawak there is a total ban on the export of both ulin and malagangai.

P. melagangai yields a medium-weight to heavy hardwood with a density of 525-920 kg/m³ at 15% moisture content. Heartwood brown with a distinct reddish tinge, sharply differentiated from the yellowish sapwood when freshly cut; grain usually fairly straight; texture moderately fine and even. Growth rings usually indistinct, sometimes indicated by fine lines of parenchyma; vessels medium-sized, solitary and in radial multiples of 2-3, tyloses abundant; parenchyma abundant, paratracheal vasicentric to aliform, occasionally confluent, conspicuous, and apotrachel in marginal or seemingly marginal bands; rays moderately fine; ripple marks absent.
Shrinkage is high, but the wood seasons fairly easily. The wood is moderately hard and very strong. It is easy to saw and plane, very durable, slightly less than that of ulin, but reportedly when used as pepper posts lasts for 20-30 years, similar to the service life of ulin posts.
See also the tables on microscopic wood anatomy and wood properties.

An evergreen, small to medium-sized tree up to 25 m tall; bole straight and cylindrical, up to 100 cm in diameter, with small, rounded buttresses up to 2 m high or with a mattress of slender roots at base; bark surface smooth to slightly flaky or fissured, dark reddish-brown to dark grey, inner bark whitish. Young twigs angular. Leaves arranged spirally, simple, entire, exstipulate. Inflorescence axillary, thyrsoid, pseudo-racemose with the lateral cymes short-stalked and 1-flowered. Flowers bisexual, 3-merous; tepals 6, in 2 rows, subequal, with a shallow tube; fertile stamens 9, those of the outer 2 whorls petaloid, those of the inner whorl each with 2 glands at base, anthers 4-locular, opening by valves; ovary superior, unilocular with a single ovule, stigma capitate. Fruit a large, 1-seeded berry, completely enclosed in and adnate to the accrescent perianth tube. Seed with a prominently, irregularly, longitudinally furrowed testa. Seedling with hypogeal germination; cotyledons not emergent, peltate; hypocotyl not developed; epicotyl with a few scales; all leaves arranged spirally.
Flowering is irregular and occurs once every 3-5 year, generally in March, April or May. Fruiting is usually recorded in September. Fruits are apparently dispersed by water, but porcupines and squirrels eat the fruits and may also disperse the seeds.
Potoxylon is very closely related to Eusideroxylon and some authors consider them to be congeneric.

P. melagangai is characteristic of primary lowland evergreen forest, mainly mixed dipterocarp forest. It is especially found on sandy-clayey alluvial soils in riverine forest and adjacent hills including limestone hills, up to 300 m altitude. It prefers well-drained but moist soils and usually occurs scattered or is rarely locally abundant.

Silvicultural characteristics of P. melagangai are probably very similar to those of Eusideroxylon zwageri, but it probably grows faster, showing at least 0.5 cm mean annual diameter increment. In its early stage of development it requires shade. P. melagangai coppices freely.

P. melagangai is rare and may be locally endangered. The protection by legislation in Sarawak seems adequate.

Increased use of P. melagangai timber is unlikely as it is rare, grows slowly and seldom reaches large dimensions.

[46]Anderson, J.A.R., 1980. A checklist of the trees of Sarawak. Forest Department, Sarawak. Dewan Bahasa dan Pustaka, Kuala Lumpur. 364 pp.
[151]Browne, F.G., 1955. Forest trees of Sarawak and Brunei and their products. Government Printing Office, Kuching, Sarawak. xviii + 369 pp.
[162]Burgess, P.F., 1966. Timbers of Sabah. Sabah Forest Records No 6. Forest Department, Sabah, Sandakan. xviii + 501 pp.
[251]de Wit, H.C.D., 1949. Spigelium Malaianum. Bulletin of the Botanic Gardens, Buitenzorg, Serie III, 18: 181-212.
[353]Fox, J.E.D., 1970. Preferred checklist of Sabah trees. Sabah Forest Record No 7. Forest Department, Sabah. 67 pp.
[422]Hassan, P. & Ashton, P.S., 1964. A checklist of Brunei trees. Forest Department, Brunei. 127 pp.
[457]Hutchinson, I.D., 1976. A summary of the occurrence, wood properties and uses of non-dipterocarp trees found in the hill forests of Sarawak. Forest Department, Kuching, Sarawak. 128 pp.
[464]Ilic, J., 1990. The CSIRO macro key for hardwood identification. CSIRO, Highett. 125 pp.
[602]Kostermans, A.J.G.H., 1955. Borneo ijzerhout (Eusideroxylon zwageri T. & B.) [Bornean ironwood (Eusideroxylon zwageri T. & B.)]. Penggemar Alam 35: 57-59.
[605]Kostermans, A.J.G.H., 1957. Lauraceae. Reinwardtia 4: 193-256.
[629]Kostermans, A.J.G.H., 1978. Potoxylon, a new Bornean genus of Lauraceae. Malayan Nature Journal 32: 143-147.
[741]Malaysian Timber Industry Board, 1986. 100 Malaysian timbers. Kuala Lumpur. x + 226 pp.
[1040]Smythies, B.E., 1965. Common Sarawak trees. Borneo Literature Bureau, South China Morning Post, Hong Kong. 153 pp.
[1050]Soerianegara, I. & Lemmens, R.H.M.J. (Editors), 1993. Plant resources of South-East Asia No 5(1). Timber trees: Major commercial timbers. Pudoc Scientific Publishers, Wageningen. 610 pp.
[1085]Symington, C.F., 1940. Eusideroxylon melagangai Symington. Hooker's Icones Plantarum 35: Tabula 3409.
[1099]Timber Research and Technical Training Centre. Unpublished data. Timber Research and Technical Training Centre, Sarawak Forest Department, Kuching.
[1222]Whitmore, T.C., Tantra, I.G.M. & Sutisna, U., 1986-1990. Tree flora of Indonesia. Checklists for Sumatra, Sulawesi, Bali, Nusa Tenggara & Timor, Maluku and Kalimantan. 6 volumes. Agency for Forestry Research and Development, Forest Research and Development Centre, Bogor.

S.P. Teo

Teo, S.P., 1998. Potoxylon Kosterm.. In: Sosef, M.S.M., Hong, L.T. and Prawirohatmodjo, S. (Editors): Plant Resources of South-East Asia No 5(3): Timber trees; Lesser-known timbers. PROSEA Foundation, Bogor, Indonesia. Database record: prota4u.org/prosea