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Eusideroxylon zwageri Teijsm. & Binn.

Family Name: Lauraceae
Common Name: Borneo Ironwood, Billian, Ironwood, Ulin, Belian

Eusideroxylon zwageri produces hard and durable timber, giving it the common name Ironwood. The timber is used for heavy construction and building of traditional houses in Borneo. Tools used to saw the wood may become blunt very quickly due to the hardness of the wood.

Full Sun: 6-8h Moderate Water Tree


Family Name
Genus Epithet
Species Epithet
Name Authority
Name Status (botanical)
Common Names
Species Summary

Classifications and Characteristics

Plant Division Angiosperms (Flowering Seed Plants)
Plant Growth Form Tree
Maximum Height 50 m


Native Distribution Borneo
Native Habitat Terrestrial
Preferred Climate Zone Tropical
Local Conservation Status Exotic

Description and Ethnobotany

Growth Form It is a tree, up to 50 m tall, with buttress up to 220 cm in diameter. Bark is grey-brown and flakes off as small subquadrangular pieces.
Foliage Leaves are elliptic to ovate (14 – 18 cm long and 5 – 11 cm wide), leathery with rounded to subcordate leaf base, obtuse to shortly acuminate leaf tip and entire leaf margin. The upper side of the leaves is smooth and hairless, while the underside of the leaves may have hairs present on the larger veins. Petiole is about 0.6 – 1.5 cm long.
Flowers Flowers occur in a dense and drooping cluster (about 10 – 20 cm long) at the axillary position. Flower is greenish, yellow or purplish, radially symmetrical and consists of a shallow flower tube. In addition, it has 6 tepals arranged in 2 whorls, 6 glandless staminodia arranged in whorls, 3 fertile stamens without glands, and a disc-like stigma.
Fruits Occurring in 1 or 2 in each panicle, the fruit is an elliptical or oval shaped drupe (about 7 – 16 cm long and 5 – 9 cm wide) and turning shiny black when mature. Each fruit contains one large seed which has a hard and furrowed seed coat.
Cultivation Young seedlings thrive in semi-shaded conditions and require full sun as they grow older.
Etymology Eusideroxylon, in greek, means iron wood, which refers to the hard timber. The species epithet is named after J. Zwager (1824-1864), a Dutch plant collector who sent specimens to Buitenzorg Botanic Garden.
Ethnobotanical Uses Timber & Products ( The timber is known as Ulin. The wood is heavy, hard, and durable, so it is often used for marine construction such as ships and wharfs, and heavy construction such as bridges, power line poles and houses. The indigenous people (Dayak) in Borneo also used the timber to build traditional houses known as longhouses. Tools used to saw the wood may become blunt very quickly due to the hardness of the wood.)

Plant Care and Propagation

Light Preference Full Sun
Water Preference Moderate Water


Mature Foliage Colour(s) Green, Red
Leaf Area Index (LAI) for Green Plot Ratio 3.0 (Tree - Intermediate Canopy)


References Kostermans, A.J.G.H. (1957). Lauraceae. Reinwardtia 4: 193–256

Image Repository



Master ID 1598
Species ID 2891
Flora Disclaimer The information in this website has been compiled from reliable sources, such as reference works on medicinal plants. It is not a substitute for medical advice or treatment and NParks does not purport to provide any medical advice. Readers should always consult his/her physician before using or consuming a plant for medicinal purposes.
Species record last updated on: 03 February 2021.