cornflower, bachelor's button, bluebottle, Centaurea cyanus(noun)

an annual Eurasian plant cultivated in North America having showy heads of blue or purple or pink or white flowers

globe amaranth, bachelor's button, Gomphrena globosa(noun)

tropical American herb having rose to red or purple flowers that can be dried without losing color

Bachelor's button(u)

a plant with flowers shaped like buttons; especially, several species of Ranunculus, and the cornflower (Centaures cyanus) and globe amaranth (Gomphrena)