In actuality, humans consume the flowers of several plants as vegetables, including broccoli. The head of broccoli is actually the plant's buds. Left intact with the roots, these buds open to reveal small yellow flowers. In addition to the familiar green variety, it is available as a purple plant. Broccoli is a member of the Brassicaceae family, and closely related to cabbage, kale and bok choy, according to About.com.