Brassica oleracea is a plant species that includes many common foods as cultivars, including cabbage, broccoli, cauliflower, kale, Brussels sprouts, collard greens, savoy, kohlrabi, and gai lan.
In its uncultivated form, it is called wild cabbage, and is native to coastal southern and western Europe. A hardy plant in its uncultivated form, its high tolerance for 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, and the windswept coast on the western side of the Isle of Wight. Wild B. oleracea is a tall biennial plant that forms a stout rosette of large leaves in the first year. The leaves are fleshier and thicker than other Brassica species—an adaptation that helps it store water and nutrients in its difficult growing environment. In its second year, it uses the stored nutrients to produce a flower spike 1 to 2 meters (3–7 ft.) tall with numerous yellow flowers.
The cultivars of B. oleracea are grouped by developmental form into seven major cultivar groups, of which
In places such as the Channel Islands and Canary Islands, where the frost is minimal and plants are thus freed from seasonality, some cultivars, known as Jersey cabbages, can grow up to 3 m tall. These "tree cabbages" yield fresh leaves throughout the year, are perennial, and do not need to be destroyed at harvest as with a normal cabbage. Their woody stalks are sometimes dried and made into walking sticks.
All contemporary cabbage cultivars were created by human selective breeding from a wild cabbage plant. Some of the leafy cabbages are grown as annuals. The bigger variety are biannuals, who will go to seed in the 2nd year.