Description from Flora of China
Roots much thickened, fusiform, branched. Stems twining, yellow-green or green, more than 2 m, branched, subglabrous or sparsely white hirsute. Leaves on main stems and major branches alternate, those on branchlets subopposite; petiole 1-6 cm, shortly white hirsute; blade abaxially gray-green, adaxially green, ovate or ovate-oblong, 2.5-15 × 1-9 cm, abaxially densely white hirsute, adaxially sparsely white hirsute, base deeply cordate to rounded, margin entire to shallowly crenate, apex shortly acuminate. Flowers solitary, terminal, or opposite leaves; pedicels 1-4 cm, hispidulous. Calyx tube adnate to whole ovary, semiglobose, obscurely 10-ribbed, hispidulous; lobes distant from each other, linear-oblong or linear-lanceolate, 8-17 × 2-3 mm, both surfaces white lanate, margin wavy, apex acute or ± obtuse; veins obscure. Corolla yellow-green at lower and middle parts, purple-red at upper part, broadly campanulate, ca. 2 × 2 cm, outside hirsute apically, shallowly 5-lobed; lobes triangular. Filaments slightly dilated at base; anthers ellipsoid, ca. 5 mm, glabrous. Capsule semiglobose or subglobose below, conical and rostrate above, 1.5-5 cm in diam., rostrum ca. 4 mm. Seeds numerous, yellow-brown, ellipsoid or ovoid, wingless, smooth. Fl. and fr. Jul-Oct.
Forests; 2300-3200 m. S Xizang (Nyalam) [Bhutan, N India, N Myanmar, Nepal].