Annual herbs. Stem dichotomous, glabrous to sparsely pubescent. Leaves entire or lobed, opposite. Bracts free. Flowers small, in cymose heads or corymbs or solitary in the axil of the dichotomies, white, lilac or pinkish-blue. Calyx limb small, enlarged in fruit, variously lobed, regular or irregular, persistent. Corolla 5-lobed, infundibuliform or salver-shaped, gibbous or spurred at the base. Stamens 3, rarely less. Stigma 3-fid. Fruit 3-locular, 2 of the locules sterile and sometimes fused with each other, the third 1-seeded.