A long-lived vine, with tuberous roots, that grows up to 15 m in height. Its younger stems are square in cross-section and bear oppositely arranged leaves on stalks up to 6 cm long. Its leaves are variable in shape but their margins are usually entire or only slightly toothed. Its blue, violet or purple trumpet-shaped flowers (3.5-4.5 cm long and 6-8 cm across) have a pale yellow or whitish coloured throat. Each flower is borne on a short stalk (about 2 cm long) and has two leafy bracts (20-50 mm long) at its base. Its fruiting capsules, when present, are rounded with a tapered beak (up to 3 cm long).