Biennial, perennial or sometimes annual, succulent herbs. Leaves usually opposite and decussate, connate at the base, the lower set close together; uppermost bract-like; lamina entire or rarely pinnatifid; margin entire, crenate or serrate. Inflorescence terminal, composed of cymes arranged in a panicle, corymb or thyrse. Flowers 4-merous, erect, relatively large and showy. Corolla lobes united below into a tetragonous tube, this rounded and swollen at the base and usually constricted above; lobes usually apiculate. Stamens 8. Carpels 4, ± connate at base. Nectariferous scales semi-circular to linear.