Roots narrowly cylindrical, 20-30 × 0.5-1 cm. Stems twining, yellow-green or green, more than 1 m, branched, sparsely villous or subglabrous. Leaves alternate, or opposite on branches; petiole 2-5 cm; blade gray-green abaxially, green adaxially, ovate to broadly ovate, 2-5.5 × 2.4-4 cm, abaxially sparsely villous, base cordate with a broad obtuse or subsquare sinus, margin crenate or serrate, apex obtuse or acute. Flowers axillary or opposite leaves; pedicels 1-2.5 cm, glabrous. Calyx tube semiglobose; lobes inserted at middle, triangular or lanceolate, 8-15 × 3.5-5.5 cm, glabrous or sparsely ciliate, apex acute, separated by narrow acute sinuses. Corolla white, campanulate, 7-8 × 6-9 mm, glabrous or ciliate; lobes triangular, equaling tube. Filaments slightly dilated at base, ca. 3 mm; anthers ca. 2 mm. Capsule semiglobose below, conical and rostrate above, 8-11 mm in diam., superior part very short, 2.5-3.5 mm. Seeds numerous, brown-yellow, ovoid, slightly compressed, ca. 1 × 0.5 mm, minutely foveolate. Fl. and fr. Jul-Oct.
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