Description from Flora of China
Cinchona gratissima Wallich in Roxburgh, Fl. Ind. 2: 154. 1824; Mussaenda luculia Buchanan-Hamilton ex D. Don, nom. illeg. superfl.
Shrubs or small trees, to 5 m tall, with thin pale brown bark; branches somewhat flattened to subterete, pilosulous [to glabrous], sometimes with sparse elliptic lenticels. Petiole 0.8-2 cm, pilosulous to glabrous; leaf blade drying papery or thinly leathery, elliptic, lanceolate-elliptic, lanceolate, or elliptic-oblong, 5-15 × 2-6 cm, adaxially glabrous, abaxially pilosulous at least along principal veins, base cuneate or acute, apex acute to acuminate; secondary veins 8-12 pairs, sometimes with pilosulous domatia; stipules lanceolate to narrowly lanceolate, 6-8 mm, glabrous to strigillose, acute to acuminate. Inflorescence corymbiform, many flowered, villosulous to pilosulous; peduncle 2-3 cm; branched portion 3-5 × 6-8 cm (not including corollas); bracts linear to narrowly ligulate, 4-7 mm, acute; pedicels 4-5 mm. Calyx glabrous to densely hirtellous; ovary portion obovoid, 3-4 mm; lobes lanceolate, oblanceolate, or narrowly ligulate, 10-16 mm, acute. Corolla red, outside glabrous; tube 30-50 mm, slenderly cylindrical; lobes suborbicular to broadly elliptic, 11-12 × 12-15 mm, rounded. Capsule 1-2 × 1-1.5 cm, pilosulous to glabrous; seeds 2-3 mm, spongy-reticulate. Fl. and fr. Apr-Nov.
W. C. Chen (in FRPS 71(1): 239. 1999) distinguished this from other species of Luculia in part by its villous pubescence on the calyx and hypanthium, but some individual specimens seen vary from densely pubescent to glabrous. The pollination biology of this species was studied by Murray (Ann. Bot. 65: 691-698. 1990).
Forests or thickets on mountains; 800-2400 m. Xizang (Mêdog), Yunnan [Bhutan, NE India, Myanmar, Nepal, Thailand, Vietnam].