Eusideroxylon zwageri Teijsm. & Binn., Natuurk. Tijdschr. Ned. Ind. 25 (1863)

Synonyms
Eusideroxylon borneense Fern.-Vill.
Salgada lauriflora Blanco

Diagnostics
Mid-canopy tree up to 40(-50) m tall and 150(-220) cm dbh. Stipules absent. Leaves alternate, simple, penni-veined, glabrous to slightly hairy below. Flowers ca. 2.6 mm diameter, white-yellow, placed in panicles. Fruits ca. 84 mm long, grey-green, stony drupes.

Description
An evergreen tree of up to 40(-50) m tall; bole straight, branchless for up to 20 m but usually less, sometimes slightly fluted at the base, up to 150(-220) cm in diameter; buttresses many, small, rounded, giving the base an elephant-foot like appearance, in moist places the base often characteristically set with a mattress of slender rootlets; bark surface red or grey-brown with thin cracks, debarking in small scab-like subquadrangular pieces which are turned up at the lower side; exudate absent; crown dense, globular; twigs smooth, slightly angular, tomentellous. Leaves arranged spirally, simple, entire, leathery, elliptical to ovate, 14-18 cm x 5-11 cm, base rounded-subcordate, the apex obtuse to shortly acuminate, upper surface glabrous, lower surface hairy on the larger veins; petiole 6-15 mm; stipules absent. Inflorescence axillary, paniculate, dense, drooping, 10-20 cm long, densely short-hairy. Flowers bisexual, actinomorphic, on a 3-11 mm long pedicel; perianth tube shallow, tepals 6, in 2 whorls, imbricate, caducous, 3-3.5 mm long, greenish, yellow or purplish, puberulous outside; stamens without glands, in 4 whorls, in the outer 2 whorls staminodial and petaloid, 1.5 mm long, yellowish with a purple tip, ciliate, those of the third whorl fertile, thick, with minute red or white anthers with a pink hue, anther cells 4, in 1 horizontal row, the central 2 extrorse, the lateral 2 sublatrorse, stamens of the inner whorl staminodial, subulate, small; ovary superior, sessile, unilocular, with a single ovule, tapering into the subulate style; stigma small, discoid. Fruit drupaceous, on a thick pedicel, 1 or 2 in each panicle, completely included in and adnate to the accrescent perianth tube, ellipsoid to ovoid or globular, 7-16 cm x 5-9 cm, glossy black at maturity, containing a single seed. Seed very large, seed-coat very hard, furrowed, brittle, pale bony; embryo very small. Seedling with hypogeal germination; cotyledons often partly fused, succulent but tough and long persistent; internodes sparsely adpressed pubescent; leaves all arranged spirally, conduplicate or induplicate when young, provided with a lateral branch in each axil. [from PROSEA]

Ecology
Ulin is a constituent of primary or old secondary tropical rain forest. It thrives in a climate with an average annual rainfall of 2500-4000 mm. It prefers well-drained soils in valleys or on hillsides or even low ridges when soil moisture is sufficient. It is found from sea-level up to 500(-625) m altitude. Ulin generally occurs on sandy soils of Tertiary origin, on clay-loam soils or on sandy silt-loam soils, but large specimens have also been found on limestone. Ulin occurs scattered or gregarious and is often the dominant canopy species. It sometimes forms almost pure stands. In Sumatra the 'ironwood forest' is recognized as a distinct forest type characterized by an exceptionally low species diversity. Ulin occurs also in mixed dipterocarp forest and has been found associated with Koompassia, Shorea, and Intsia species. Capable of regeneration via sprouts when cut. Tendency to dominate forest stands. Seed dispersal is apparently often by water; rich pockets of ulin forest are often found at places where the fruits wash ashore in large quantities along rivers. Procupines may also disperse the seeds.

Uses
Ulin is one of the heaviest and most durable timbers of South-East Asia. As such, it is preferably used in marine constructions such as pilings, wharfs, docks, sluices, dams and ships (keels, ribs and decking), or in heavy constructions such as bridges, power line poles, masts, piles and house posts. Ulin is also used for the traditional houses ('longhouses') of the Dayak in Borneo. Another major use of ulin is for roof shingles ('sirap') which are reported to last 50 years to more than a century. Less important is the use of ulin as frame, board, for heavy duty flooring, floodgates, road pavement and foundations, railway sleepers, fencing, printing blocks, vehicle bodies, sleds for log skidding, furniture, chopsticks, blowpipes, poles (in pepper cultivation) and survey pegs. The wood is not suitable for plywood or particle board production. The large fruits are poisonous and pulverized fruits have been used medicinally against swellings.

Distribution
Eastern and southern Sumatra, Bangka, Belitung, Borneo and the Sulu archipelago and Palawan (the Philippines).

Local names
Borneo: Belian, Belian timun, Betian, Talion bening, Tebelian geriting, Telianoii, Teluyan, Ulin, Ulin bening, Ulion.
English: ironwood, billian.
French: Bilian, bois de fer.
Indonesia: belian (general), onglen (Sumatra), tulian, tebelian (Kalimantan).
Malaysia: belian (Sarawak, Sabah), tambulian (Sabah), im muk (Cantonese, Sabah).
Philippines: tambulian, sakian, biliran (Sulu).