Broccoli is an edible green plant in the cabbage family whose large, flowering head is eaten as a vegetable. The word broccoli comes from the Italian plural of broccolo, which means "the flowering crest of a cabbage", and is the diminutive form of brocco, meaning "small nail" or "sprout". Broccoli is a result of careful breeding of cultivated leafy cole crops in the northern Mediterranean starting in about the 6th century BC. Since the Roman Empire broccoli has been considered a uniquely valuable food among Italians. It was first introduced to the United States by Italian immigrants, but did not become widely known there until the 1920s.