Brassica oleracea, or Wild Mustard, is a species of Brassica native to coastal southern and western Europe, where its tolerance of salt and lime and its intolerance of competition from other plants typically restrict its natural occurrence to limestone sea cliffs, like the chalk cliffs on both sides of the English Channel.
Although B. oleracea is believed to have been cultivated for several thousand years, its history as a domesticated plant is not clear before Greek and Roman times, when it is known to have been a well-established garden vegetable. Theophrastus mentions three kinds of this species: a curly-leaved, a smooth-leaved, and a wild-type. It has been bred into a wide range of cultivars, including cabbage, broccoli, cauliflower, and more, some of which are hardly recognisable as being members of the same genus, let alone species. The historical genus of crucifera, meaning four-petalled flower, may be the only uniting feature beyond taste. It has become established as an important human food crop plant. According to the Triangle of U theory, B. oleracea is very closely related to five other species of the genus Brassica.