Which one of the following vegetables is not obtained from wild cabbage?

Wild cabbage (Brassica oleracea) is the common ancestor of several diverse vegetables developed through selective breeding over millennia [t2][t6]. These cultivars, often referred to as 'cole crops', include broccoli (selected for flower buds), kale (selected for leaves), and kohlrabi (selected for its swollen stem) [t2][t3][t5]. Other derivatives include cauliflower, Brussels sprouts, and collard greens [t3][t5]. In contrast, lettuce is not derived from wild cabbage; it belongs to a completely different plant family, Asteraceae, and is scientifically classified as Lactuca sativa [t4]. While cabbage and lettuce may appear physically similar due to their leafy heads, they are unrelated species with distinct nutritional profiles and botanical origins [t4]. Therefore, lettuce is the only vegetable among the options that is not a cultivar of Brassica oleracea.