(species Brassica oleracea, Acephala group), loose-leafed, edible plant derived from the cabbage of the mustard family (Brassicaceae) and including several forms. Common, or Scotch, and Buda kale are among the hardiest of vegetable crops. The plant produces a strong-growing rosette of long-petioled, elongated leaves with wavy to frilled margins. In a long growing season the main stem reaches a height of 60 cm (24 inches) or more. The plant may be harvested by cutting off the entire rosette before the stem has elongated, or (especially in areas with long, cool growing periods) the individual lower leaves may be removed progressively as the main stem elongates. Kale is grown mainly for autumn and winter harvest, because cold improves its eating quality and its hardiness permits harvest of fresh greens after most fresh vegetables have become unavailable. It is usually served as a cooked vegetable and is a good source of vitamin A. The leaves of fresh kale should be unwilted and dark bluish green in colour.