Annual or perennial herbs; stems slender, usually prostrate, spreading, glabrous or pubescent, sometimes rooting at nodes. Leaves opposite or subverticillate; petiolate; stipules small, scarious, often persistent or falling off rapidly; blade glabrous to villous with often glandular hairs. Inflorescences few-flowered mono- or dichasial cymes; bracts scarious. Sepals 5, free, herbaceous with scarious margin; petals (0-3)5, white, often deeply bifid, sinus sometimes laciniate; stamens 2-5, filaments somewhat connate, flattened; ovary ovoid, sessile or substipitate, 1-locular, ovules few, campylotropous on free central placenta, 3 styles united at base. Fruit an ovoid, 3-valved capsule; seeds 1-numerous, globose-reniform, cochleate or hippocrepiform, usually granular or tuberculate, rarely smooth.