Annual or perennial herbs, rarely undershrubs, of very various habit. Leaves opposite or alternate or whorled, simple, often fleshy, stipules wanting or scarious. Flowers regular, usually hermaphrodite, solitary or fascicled or cymose. Calyx free or adnate to the ovary, 4–5-celled or -partite, imbricate. Petals either narrow and numerous, or 4–5 and small, or altogether wanting. Stamens perigynous or rarely hypogynous, few or many; filaments free or connate at the base. Ovary superior or inferior, 2–5-celled; styles as many as the cells, free or united at the base; ovules either solitary in the cells and basal, or numerous and axile. Fruit generally a capsule with loculicidal or transverse dehiscence, more rarely drupaceous or separating into 1-seeded cocci. Seeds solitary or many, usually compressed; albumen scanty or copious; embryo slender, curved round the albumen, terete.

A large order, comprising 22 genera and nearly 500 species, mostly tropical or sub-tropical, and especially plentiful in South Africa; rare or absent in cold climates. The properties of the order are unimportant. Many species of Mesembryanthemum have showy flowers, and are cultivated in gardens; and Tetragonia is occasionally used as a pot herb. The remaining genera are mostly insignificant weeds. Both the New Zealand genera are widely distributed, although much more numerously represented in South Africa than elsewhere.