Hopea fluvialis (PROSEA)

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Plant Resources of South-East Asia
List of species

Hopea fluvialis P. Ashton

Protologue: Gard. Bull. Sing. 19: 254, pl. 1 (1962).

Vernacular names

  • Brunei: merawan ayer
  • Malaysia: merawan ayer (Sarawak).


South-eastern Kalimantan, south-eastern Sabah, north-eastern Sarawak and Brunei.


The timber is used as merawan, but because of the often crooked shape of the bole, not of great commercial interest.


  • A small to medium-sized tree of up to 25 m tall, bole often of poor shape, with a diameter of up to 70 cm and small buttresses, flying buttresses present, stilt roots absent, bark surface smooth, inner bark brown to cream, sapwood pale yellow, medium hard, with a gradual transition to the pale brown heartwood; young parts shortly densely pale grey-brown tomentose.
  • Leaves lanceolate to ovate, 7-12 cm × 3-5 cm, chartaceous to thin leathery, base narrowly or broadly cuneate, subequal, acumen slender, up to 1.5 cm long, venation dryobalanoid, midrib raised above, secondary veins about 10 pairs with long smaller veins in between, slender, arched at 60-80°, the basal pair continuing as intramarginal veins to one-third up the margin, tertiaries reticulate, indistinct.
  • Stamens 15, ovary ovoid, glabrous, style filiform, tapering, as long as the ovary.
  • 2 longer fruit calyx lobes up to 5.5 cm × 1 cm, tapering into an expanded but unthickened and hardly saccate base, 3 shorter ones unequal, 1-2.5 cm long, acute, cupped and enveloping the nut.

H. fluvialis is locally abundant on rich clayey river banks up to 300 m altitude.

Selected sources

30, 31, 258, 748.

Main genus page


  • K.M. Kochummen (selection of species),
  • F.T. Frietema (selection of species)