Pentarrhinum insipidum is a slender, fast-growing, branching vine that sprouts from a woody, perennial rootstock and produces stems 2-3 m long. It scrambles over other shrubs or twines itself around trees and bushes. All the parts are delicately covered with hairs. The leaves are simple, stalked and broadly ovate to heart-shaped with a deep cordate base and pointed tip; the leaf blade is 200-650 x 15-50 mm; the stalks are 15-50 mm long, usually pointing downwards.

The corollas of the flowers are reflexed, arranged in lateral pseudo-umbels which hang from the nodes and are small, greenish to yellow, with the basal parts of the corolla sometimes tinged purple to brown. A white form occurs in the coastal areas of KwaZulu-Natal. The corona is white, beige, yellow or orange to brown-greenish, fleshy with a horn-like appendage. Flowers are fragrant and aromatic and are produced from November to April. The fruit is usually a solitary follicle, somewhat inflated, lance-shaped with an uneven, warty surface, 55-85 x 15-20 mm, with teeth 2-4 mm long. The seed is 6.0-6.5 x 4 mm, tightly packed, flat, with a marginal wing and with a tuft of white hairs at the one end.