Annual or perennial herbs, or subshrubs; stems often jointed and swollen at nodes. Leaves opposite and decussate, or whorled, simple, entire; exstipulate or less often with small, scarious stipules, often connate at base; often sessile or indistinctly petiolate, petiole often amplexicaul. Inflorescence a terminal, solitary flower, or a dichasial cyme or umbel. Flowers regular, bisexual, rarely unisexual; sepals 4-5, imbricate, free or united in a tubular, 4- or 5-toothed calyx, persistent; petals as many as sepals or sometimes some or all absent, free or nearly so, sometimes bifid and clawed; stamens in 1 or 2 whorls, sometimes in part absent, filaments free, basally united or epipetalous ones adnate to base of petal, anthers 2-locular, versatile, longitudinally dehiscent; ovary superior, sessile or shortly stipitate, 1(-5)-locular, ovules 1-numerous, campylotropous, placentae basal, central or free central, style 1, 1 lobed or 2-5 stigmas, or styles 2-5, free or united at base. Fruit a capsule, valvate or dehiscing by 2-5 apical teeth; seeds usually numerous, small, with mealy endosperm, embryo curved around perisperm.
Cosmopolitan present, Guianas present
Approximately 2200 species in 86 genera, cosmopolitan, but most widely distributed in temperate regions of the northern hemisphere (with a center in the Mediterranean and Irano-Turanean regions), rarely indigenous to the tropics; in the Guianas 2 species in 2 genera.