Cabbage or headed cabbage (comprising several groups of cultivars of Brassica oleracea) is a leafy green or purple biennial plant, grown as an annual vegetable crop for its dense-leaved heads. Closely related to other cole crops, such as broccoli, cauliflower, and brussels sprouts, it descends from B. oleracea var. oleracea, a wild field cabbage. Cabbage heads generally range from 0.5 to 4 kilograms (1 to 9 lb), and can be green, purple and white. Smooth-leafed firm-headed green cabbages are the most common, with smooth-leafed red and crinkle-leafed savoy cabbages of both colors seen more rarely. It is a multi-layered vegetable. Under conditions of long sunlit days such as are found at high northern latitudes in summer, cabbages can grow much larger. Some records are discussed at the end of the history section.