Cornflower (Bachelor’s Button; Blue Bottle)
A much-branched herbaceous annual. Flowerheads about 1 inch across with a vase-shaped involucre (the bracts), in cornflower blue, pink, or white. A member of the thistle tribe, this composite lacks true ray florets; instead, the outer florets of each head have enlarged corolla tubes that at a glance look something like the strap-shaped extensions of true ray florets. Blooms May-September. Leaves narrow, linear, sharply pointed, alternate.
Similar species: There are 10 Centaurea species recorded for our state. Of special concern is the invasive spotted knapweed, C. stoebe. Its principal leaves are deeply lobed, the florets are light purple to pinkish purple or rarely white, the flowerheads more thistlelike.