Description from Flora of China
Trees, lofty, to 45 m tall. Bark gray or brown, shallowly flaky, not longitudinally fissured or only at base. Branchlets glabrous or persistently buff pubescent; leaf buds obtuse, stout, glabrous, setose, or woolly. Stipules green or red, lanceolate, to 15 cm, glabrous or pubescent outside (always stellate pubescent on young trees); petiole glabrous; leaf blade broadly ovate, 16-28 × 10-15 cm, leathery, abaxially sparsely or densely golden-buff stellate pubescent, adaxially initially white strigose, sometimes glabrescent, lateral veins 16-19 pairs conspicuously raised abaxially, base rounded or somewhat cordate, margin entire or sinuate-crenate in distal half, apex acute. Racemes axillary, 8-10 cm, 2-5-flowered. Calyx segments: 2 rather long and linear, 3 shorter and triangular. Petals reddish, sweetly scented, narrowly elliptic, 5-6 cm, with dense squamate hairs, margin slightly reflexed, apex obtuse. Stamens (25-)30; anthers linear to lanceolate, ca. 5 mm, sagittate at base, coherent; connective appendages aristate; filaments filiform, dilated at base. Ovary narrowly ovoid, sericeous-tomentose, 3-loculed, with 2 ovules per locule; style finely terete, with long silky hairs on lower half. Nut ovoid, densely yellowish gray tomentellate; calyx tube to 3.5 cm in diam.; winglike calyx segments red, linear-lanceolate, to 19-23 × 3-4 cm, leathery, stellate-tomentellate, 3-5-veined, apex rounded. Fl. May-Jun, fr. Dec-Jan of following year.
Still locally abundant in the E Himalayan foothills, this species is now rare in Yunnan, its distribution affected by habitat loss. The wood is heavy and is used for building houses. The tree is a source of a balsam used for caulking boats.
This species is very variable at the extremes of its range: China, N Vietnam, and Indonesia (Java). Dipterocarpus macrocarpus was recognized on account of its dense tomentum on twigs, leaf buds, and leaf abaxial surface, and D. mannii on account of its somewhat smaller parts and ca. 25 stamens. Two varieties of D. retusus can be recognized in China, and they may co-occur in the same stand.
Humid valley rain forests, dense forests on limestone; below 1000 m. SE Xizang, SE and W Yunnan [India, Indonesia, Laos, Malaysia, Myanmar, Thailand, Vietnam].