Herbs. Stems usually thickened and jointed at the nodes. Leaves opposite or apparently whorled, often connate basally; stipules present or absent. Flowers usually bisexual, regular. Sepals 4–5, free or connate, persistent, imbricate in bud. Petals 4–5, sometimes absent, imbricate in bud. Stamens up to 10. Ovary superior, usually 1-locular with basal or free central placentas, rarely multi-locular with axile placentas. Fruit a capsule or nut. 80 gen. cosmop. mainly N. hemisphere.