Description from Flora of China
Trees to 5 m tall, all parts glabrous. Branches brown when young, striate with age. Petiole 0.4-2 cm, swollen; leaf blade narrowly oblong-lanceolate, 10-39 × 2.5-8 cm, leathery, midvein adaxially depressed, secondary veins 14-20 on each side of midvein and inconspicuous, base cuneate, apex acuminate to acute. Inflorescences axillary, 1-flowered. Pedicel 5-10 mm, bracteolate at base. Sepals broadly ovate, ca. 1.5 × 1 cm. Petals green turning brownish yellow, leathery; outer petals oblong-lanceolate, 5-6 × 1-1.5 cm; inner petals elliptic, ca. 1.5 × 1 cm. Stamens linear but obconic when dry, ca. 1.8 mm; connectives apically flat to very slightly convex, puberulent. Carpels cylindric, pubescent; ovules 2 per carpel; styles slender; stigmas entire. Monocarps to 20, ovoid, 1-1.7 × 0.5-0.8 cm. Seeds 1 or 2 per monocarp, pale reddish brown, ovoid, slightly compressed. Fl. May-Nov, fr. Nov-Feb.
R. M. K. Saunders (in litt.) believes that Goniothalamus gardneri is endemic to Sri Lanka and that the Chinese and other material so named has been misidentified. The Sri Lankan material differs by the sparsely puberulent stems, slightly smaller sepals (0.8-1.2 cm), and shorter petals (outer 2.4 to less than 5 cm, abaxially puberulent; inner 0.9-1.4 cm).
Densely forested slopes; 200-700 m. Hainan [India, Sri Lanka, Vietnam].