Annual or sometimes short-lived perennial, with twining to decumbent-creeping, slender, somewhat angular stems 2-5 m long. Leaves are broadly ovate or nearly circular, 4-15 x 4.5-14 cm, base heart-shaped, margin entire or 3-lobed. Inflorescences axillary, 1- to few flowered. Petals pale to bright blue with whitish tube, fading to pinkish in age, funnelform, 5-6 cm. Seeds black, ovoid-trigonous, 5-6 mm. Capsules ovoid to depressed-spherical, 7-8 mm high, 8-12 mm thick, 3-6-seeded. Seeds 4.5-6 mm long, black or brown. The black seeds have led to many of its common names.