Isopteris penangiana Wallich ex Benn.

An evergreen, small to medium-sized tree up to 30(-40) m tall; bole usually columnar, up to 50(-60) cm in diameter, sometimes with buttresses up to 1(-2) m high; bark surface smooth, lenticellate, pale greenish-grey to brown, inner bark granular, pale greenish-yellow to yellowish-brown, exuding a yellowish sticky juice which turns reddish upon exposure; crown conical to hemispherical. Leaves alternate, simple, entire, with small glands along the margin and at the top; stipules caducous. Flowers in an axillary or terminal, puberulous panicle, fragrant, zygomorphic; sepals 5, free, unequal; petals 5, free, very unequal, white, one of them saccate at base; stamens 6, united in a tube; ovary superior, 3-locular with 2 pendulous ovules in each cell one of which is aborted in fruit, style simple. Fruit a schizocarp, splitting into 3 flat, winged, 1-seeded samaras. Seedling with epigeal germination; cotyledons emergent, fleshy; hypocotyl elongated; first pair of leaves opposite, subsequent ones alternate, all leaves white puberulous below.

Flowers and fruits have been collected throughout the year but the phenology may be more restricted on a local scale. The flowers are presumably insect-pollinated and the winged fruits are wind-dispersed.

There may be 2 ecological forms within T. hypoleucum, one growing on nutrient-poor soils and the other one on nutrient-rich soils. T. hypoleucum occurs scattered in a wide range of lowland to submontane, evergreen forest types like peat-swamp, freshwater swamp, kerangas, alluvial and mixed dipterocarp forest. It is sometimes encountered in disturbed forest.

T. hypoleucum can be propagated by seed. The samaras are the unit of sowing and the germination rate is about 85% in 19-47 days.

Ornamental: The tree may be suitable for ornamental purposes. Shade or shelter: The tree may be suitable for shade purposes.

Timber: The wood of T. hypoleucum has been used for furniture.