Cornflowers used to be a common arable weed, but have declined in recent years and are now only rarely found in the wild.
There are two species of cornflower: the annual one (Centaurea cyanus) is smaller, has bright blue outer florets and reddish inner ones, and has bracts with silvery jagged-toothed edges. The perennial cornflower (Centaurea montana) is larger and more robust.

Flower side-on, showing jagged-toothed bracts		Stem leaves		Seeds