# Eusideroxylon

Eusideroxylon is a genus of evergreen trees of the family Lauraceae. The genus is monotypic, and includes one accepted species, Eusideroxylon zwageri. It is known colloquially in English as Bornean ironwood, billian, or ulin.
It is native to Borneo and Sumatra, where it grows in lowland rain forests.
Eusideroxylon are hardwood trees reaching up to 50 metres in height with trunks over 2 metres (6 ft 7 in) in diameter, producing commercially valuable timber. The wood of E. zwageri is impervious to termites, and can last up to 100 years after being cut. Due to extensive logging, it is listed as vulnerable in the IUCN Red List.

## Description

Eusideroxylon are canopy tree species with erect or spreading branches and extremely durable and decay-resistant wood.
Eusideroxylon zwageri is a slow growing (0.5 metres per year) tall evergreen tree with a straight bole (usually host to Cassytha, a parasitic vine with leaves reduced to scales, up to half of the tree's height). It is slightly fluted at the base, up to 150–220 cm in diameter. The trunk has many small, rounded buttresses that give the base an elephant-foot like appearance. Individual trees may reach an age of 1,000 years or more. Common commercially exploitable trees attain a height of 30 or more metres (100 ft) with trunk diameters of exploitable trees up to 92 cm (36 inches). Protected trees are towering giants of the forest attaining a height of up to 50 metres and a diameter of 220 cm – though height is routinely reduced by lightning strikes. An Ulin tree discovered in 1993 in Kutai National Park, is one of the largest plants in Indonesia. It is an estimated 1,000 years old, and has increased its diameter from 2.41 to 2.47 metres in the 20 years since its discovery. Its height was however reduced from some 30 metres to only 20 after a lightning strike. Another at Sangkimah in the west of the park has a diameter of 2.25 metres and a height of some 45 metres.
The color of the flowers is pale yellow to yellow. The flower is hermaphrodite, actinomorphic, with 6 tepals, distributed in two whorls that overlap. There are six staminodes, three stamens, and a simple pistil that consists of one carpel. Pollination is done by bees and other insects. The fruits are drupes, varying in size and shape from oblong to ovate or sub-cylindrical to asymmetric elongated or rounded. They are 8–13 cm long, 4–5 cm in diameter, and weigh 90g-170g. Seed dispersal is by vertebrate animals such as birds, monkeys, bats and rodents, for which the fruits are an important food source.
The trees' leaves are dark green, simple, leathery, elliptical to ovate, 14–18 cm long (5.5–7.5 inches) and 5–11 cm wide (2–4 inches), and are alternate, rarely whorled or opposite, without stipules and petiolate. The leaf blade is entire (unlobed or lobed in Sassafras) and occasionally with domatia (crevices or hollows serving as lodging for mites) in axils of main lateral veins (present in Cinnamomum). Young leaves are reddish brown to yellowish red. They have a generous layer of wax, making them glossy in appearance, and are narrow, pointed oval in shape with an apical mucro, or 'drip tip', which enables the leaves to shed excess water in a humid environment.
Timber segments collected from 15 logged stumps in Kubah National Park, Sarawak, Malaysia, found that E. zwageri can live more than 1000 years and that the growth rate of this species is very slow, with a mean radial growth rate of 0·058 cm y-1. The cutting of old trees of E. zwageri results in the species being replaced by faster growing species. The long life span and reduced growth rate of this species may be a result of its dense and durable wood containing abundant defensive compounds.

## Etymology

The name Eusideroxylon is Latinized Greek, derived from Greek sideros meaning iron, xylon meaning wood, with the prefix eu- meaning good, true, original. The name of the genus thus means "true iron wood".

## Habitat

Eusideroxylon zwageri seedlings require some shade, while older trees need plenty of light. It can be found in valleys and on hillsides and even on low ridges when soil moisture is sufficient at elevations between sea level and 625 m. The standing timber volume of trees with a diameter of over 50 cm may be as much as 90–112 m$^3$.

## Silviculture

Eusideroxylon zwageri has a very slow growth rate of mean radial growth of 0.058 cm per year. It is a canopy species in primary forests. The species is considered unsuitable for large-scale plantations due to slow growth and inadequate seed and seedling supply. Manual selection of trees in natural forests is common.

## Properties

The heartwood when cut is coloured light brown to almost bright yellow. During the aging process the heartwood darkens to deep reddish brown, very dark brown or almost black. The sapwood is bright yellow when cut, and darkens slightly. The wood texture is fine and even, with a straight grain or only slightly interlocked. The timber retains a pleasant lemon odour. This odour, along with the woods' natural high lustre, make it prized by cabinet-makers and fine furniture craftsmen.
The wood is dense, and texture is moderately fine to fine and even. Also attractive to users is the resistance to insects, bacteria, fungi and marine borers. The wood has anti-bacterial properties (for local medicinal use) Vessels are diffuse-porous, medium-sized and generally evenly distributed, arranged in short radial rows (2–3 vessels). Moderate abundancy of aliform paratracheal parenchyma. Growth rings boundaries are indistinct or absent. Tyloses are often present.
The wood has a radial shrinkage rate of 2–4.5% and a tangential shrinkage rate of tangential 4.5–7.5%. The timber dries slowly, and care is needed to avoid checks and splits. The wood is famed for its easy working characteristics, despite high density. The wood planes, bores and turns cleanly, producing smooth and often lustrous surfaces. Nailing requires pre-bores prior to nailing. Saw blades and other cutting instruments are moderately blunted during working the timber. The wood is apparently difficult to glue with synthetic resins.
Heartwood is rated as very durable – immune to termite attack; service life of up to 100 years in direct soil contact and more than 20 years for marine work in tropical waters has been reported.

## Usage

Due to the excellent resistance to bacterial, fungal, insect and marine borer attack the wood is highly prized for many outdoor uses, especially as decking. Additionally, the wood's high density and easy workability lend it to particularly desirability in maritime structures, dock construction and ship building, especially Indonesia's pinisi sail-boat. Common local uses include: House construction, door construction, water butts and troughs, boat building (Pinisi), tools, tool handles, talisman, jewellery, medicinal slivers (for wounds, cuts, abrasions, bites and tooth-ache/infection), bridges, blowpipes and spear shafts.
Internationally, it is renowned for heavy construction such as a buffer between transportation trailers and heavy steel fabrications (such as boilers, pressure vessels, reactors and many others). It is also frequently found in dry docks as a timber to separate the hull of ships from the steel supporting stands. Other uses include use in boats and ships, industrial flooring, roofing (as shingles), fine indoor and outdoor furniture, coffin wood (esteemed by Chinese due to ability to withstand rot and insect attack) and tool handles (especially those exposed to continual high impact (the wood does not splinter and thus injure hands, eyes or endanger the operator on catastrophic failure) such as shovels, axes, block splitters, sledge hammers, heavy mallets, demolition hammers, mattocks, picks, hoes and hammers). Some expert cabinet-makers treasure an ulin-headed carpenter's mallet as an excellent intermediate density hammer face between the usual wood and a metal one and is able to quite easily tap or "whack" stubborn highly polished metal fixtures without damage to the face or the fixture.
Other sources indicate that ulin wood is often used for marine constructions such as pilings, wharfs, docks, sluices, dams, ships, bridges, but also used for power line poles, masts, roof shingles and house posts and to a minor extent as frame, board, heavy duty flooring, railway sleepers, fencing material, furniture etc.

## Conservation

The government of Indonesia and the state government of Sarawak have formally banned the export of this species. Illegal smuggling continues to be a major problem.
Conservation efforts are underway, with several countries banning imports.

## Species

* Eusideroxylon zwageri
Formerly placed here:
* Potoxylon melagangai, as Eusideroxylon melagangai