Herbs or shrubs, rarely trees. Leaves alternate, simple, usually entire; stipules present or wanting. Flowers regular, hermaphrodite. Sepals 5, rarely 4, free or coherent at the base, imbricate. Petals the same number, hypogynous or slightly perigynous, imbricate, often contorted. Stamens as many as the petals or twice as many, rarely more; filaments united below into a ring which frequently has 5 small glands at the base; anthers 2-celled, versatile. Ovary free, entire, 3–5-celled; styles the same number, distinct or more or less united; ovules 1–2 in each cell, pendulous, anatropous. Fruit either a capsule splitting into 3–5 cocci, or more rarely a drupe. Seeds 1–2 in each cell; albumen fleshy or wanting; embryo usually straight, radicle superior.

A small order, scattered over the whole world, the herbaceous species mainly temperate, the shrubby almost all tropical. Genera 14; species about 140. The common flax, Linum usitatissimum, so valuable from the tenacity of its fibre and its oily seeds, is the most important member of the order. The Peruvian Erythroxylon coca yields the important drug cocaine, and the leaves are chewed as a stimulant. The only New Zealand genus is widely distributed.