Annual or perennial herbs, glabrous or glandular-hairy; rootstock often thick and fleshy or woody. Leaves opposite, petiolate. Inflorescence cymose, with flowers solitary, paired, clustered, or commonly, in simple or compound umbels; flowers small, bisexual; upper part of perianth petaloid, bell- or trumpet-shaped, shallowly 5–10-lobed, caducous; stamens 1–4, shorter than or shortly exceeding perianth; style simple, stigma capitate; ovary shortly stalked, enclosed by non-petaloid, lower part of perianth. Fruit 3–5-ribbed, often with short, glandular hairs.