Description from Flora of China
Isotrema transsectum Chatterjee, Kew Bull. 3: 64. 1948.
Shrubs climbing. Stems angled, villous, with elongate internodes. Petiole 4-5 cm, villous; leaf blade ovate or oblong, 12-19 × 3.5-6 cm, leathery, abaxially glabrous, adaxially sparsely villous, veins palmate, 5-6 pairs from base, base deeply cordate, sinus 0.5-3 cm deep, apex acute. Flowers in axils of leafy shoots, solitary. Pedicel recurved, 4-5 cm, brown tomentose; bractlets subulate, ca. 5 × 1 mm, inserted near base of peduncle. Calyx dark brown; tube geniculately curved, abaxially sparsely pubescent; basal portion of tube ca. 25 × 10 mm; limb conic, symmetric, ca. 1.5 cm in diam., shallowly 2- or 3-lobed; lobes unequal, upper 2 large, oblong, lower 1 small, broadly ovate. Anthers oblong, ca. 2 mm. Gynostemium 3-lobed. Fruit not seen. Fl. May-Jun.