Cabbage (Brassica oleracea or variants) is a leafy green biennial, grown as an annual vegetable for its densely-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 1 to 8 pounds (0.45 to 3.6 kg), 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 difficult to trace the exact history of cabbage, but it was most likely domesticated somewhere in Europe before 1000 BC. By the Middle Ages it was a prominent part of European cuisine, although savoys were not developed until the 16th century.