Perennial herbs from a subterranean, subglobose or elongated root–tuber, laticiferous; stems herbaceous, erect or twining. Leaves alternate, sessile or petiolate. Flowers in racemes, zygomorphic. Calyx 5–lobed. Corolla either split to the base into 2 lips with the upper one 3–lobed and the lower consisting of 2 free petals, or all petals united into a tube with a 5–lobed limb. Stamens 5; filaments free or united towards the base; anthers free or apically loosely united, glabrous or ± pubescent on the back of the connective. Ovary subinferior to subsuperior, 2–locular; ovules many; style shorter than the stamens, obliquely clavate, crowned by hairs, in the upper part with a stigmatic cavity communicating with the air through a small, lateral aperture. Capsule 2–locular, dehiscing loculicidally by 2 apical, usually bifid valves. Seeds numerous.