(Jungh. ex de Vriese) L.A.S.Johnson
Gymnostoma sumatranum and the other members of this family are characterized by drooping equisetoid (meaning "to look like Equisetum") twigs, are evergreen, and monoecious or dioecious. The roots have nitrogen-fixing nodules. The foliage of this tropical angiosperm tree looks like that of gymnosperm pine trees which typically grow in temperate climates. Casuarina equisetifolia (the most well-known member of Casuarinaceae) is typified by its equisetoid appearance, whilst G. sumatranum is characterised more by its multiple rounded umbrella-shaped crowns. The stems are angular or tetrahedal in cross section (2). The stomata are not restricted to sunken grooves, (2). The female inflorescences are borne terminally (2).
In Malaysia, G. sumatranum is known as Rhu Bukit - bukit in Malaysian means "hill". The other common she-oak species in Malaysia is Casuarina equisetifolia known as Rhu laut - laut in Malaysian means "sea" and typically it grows along the seashore on sandy substrates. In Sarawak it is a protected species (5). G. sumatranum typically grows further inland. However when occurring in coastal regions, it provides good indication that the soil is dry and out of the littoral and inundation zone since G. sumatranum will not normally tolerate sandy or boggy soil.
- Dilcher, D. L. et al.. (1990) Evolution of the Casuarinaceae: morphological comparisons of some extant species. American journal of Botany. 77(3): 338-355. 1990.
- P. S. Green, Klaus Kubitzki, E. Götz, K. U. Kramer. (1990) The Families and Genera of Vascular Plants. Published by springer. 404 pages
- Jane N. Prider and David C. Christophel Distributional ecology of Gymnostoma australianum (Casuarinaceae), a putative palaeoendemic of Australian wet tropic forests. Australian Journal of Botany 48(4) 427 - 434
- Barlow, B.A., (1983). Casuarina Ecology,. Management and Utilization. edited by S.J.Midgely. pp. 10–18
- Sarawak Forestry ordinance 1998