Cauliflower is one of several vegetables in the species Brassica oleracea, in the family Brassicaceae. It is an annual plant that reproduces by seed. Typically, only the head (the white curd) is eaten. The cauliflower head is composed of a white inflorescence meristem. Cauliflower heads resemble those in broccoli, which differs in having flower buds. Brassica oleracea also includes broccoli, brussels sprouts, cabbage, collard greens, and kale, though they are of different cultivar groups. (source)