Dyera costulata aka Hill Jelutong

Dyera costulata is a large, leaf-shedding tree called hill jelutong. It belongs to the Apocynaceae family. Its native range spans southern Thailand and western Malesia. This includes Malaysia, Singapore, Sumatra, and Kalimantan. It grows in wet tropical forests, on lowlands and hills. Wild trees often stand on slopes and ridges. Some trees in regrown forest survive from the former forest.

Published size guides give a height of 164 feet [50 metres]. They give a crown width of 98 feet [30 metres]. Forest trees can reach 246 feet [75 metres]. The crown spreads wide when the tree grows in sun. The trunk lacks buttresses and can become very thick. Its diameter can reach about 10 feet [3 metres]. Branches may start 49–98 feet [15–30 metres] above the ground. These dimensions make it a tree that needs ample space.

Hill jelutong needs full sun and moist soil that drains well. It grows in sandy, loamy, and clay soils. It accepts mildly acid, neutral, and mildly alkaline ground. PFAF lists its growth rate as moderate. The tree suits the warm, wet conditions of lowland tropical regions. PFAF places it in USDA zones 10–12. Both wild and planted trees occur in its native region. Growers also cultivate it on the Malay Peninsula.

People have tapped the trunk for latex for hundreds of years. Much of this harvest comes from wild forest trees. Latex has uses in chewing gum and several manufactured materials. These include celluloid, linoleum, and coatings for electric cables. It also goes into cement, paint, and paper mixtures. People harvest the tree for timber as well. The roots can serve in place of cork. The resin-rich fruits provide fuel for torches and repel mosquitoes. They also have recorded medicinal uses, though no treatment details appear here.

PFAF lists no known edible parts and gives an edibility score of zero. Its record of latex use in gum does not establish other edible uses. The sources report no known hazards, rather than proof of safety. Long use for timber and latex once raised concern about its survival. Yet it can regrow after cutting and recover in logged forest. Useful Tropical Plants lists its conservation status as Least Concern. Seed offers a way to raise new trees. It stays viable for less than a year. A 12-hour soak can help speed germination, though pretreatment is not required.