Annual or perennial herbs or undershrubs, sometimes aquatic or semi-aquatic. Leaves opposite or verticillate, simple, stipulate, entire or serrate. Inflorescence solitary axillary or a fasciculate cyme. Flowers small, bisexual, actinomorphic, hypogynous. Sepals 3-5, rarely 2 or 6, free or basally connate, imbricate. Petals 3-5, rarely 2 or 6, free, hypogynous, imbricate. Stamens as many as or twice the number of petals in 1-2 whorls, alternating with the petals, hypogynous, free; anthers versatile, dithecous, dehiscence longitudinal. Carpels 3-5, united; ovary superior, 3-5 locular, placentation axile, ovules numerous in two or more rows on each placenta, anatropous; styles 3-5, rarely 2, free. Fruit a septicidal or a septifragal capsule. Seed and embryo straight or curved, without or with very little endosperm.