Perennial herbs. Their leaves are whole or dissected, whole-edged or toothed, the lower opposite, the upper alternate.
The flowers are nondescript, mostly greenish, yellow or purple, in long forked, paniculate or racemose inflorescences. The calyx is five-lobed or five-divided. The corolla is usually double-lobed, spherical or pitcher-shaped, with an almost double-lobed five-lobed bend and with a lower unpaired blade, turned downwards; four double-strong stamens and a glandular staminodium (in the form of scales).
The fruit is an ovoid or almost spherical multi-seeded capsule, opening with two leaves; the seeds are oval, with transverse wrinkles.