Bachelor’s Button (Centaurea cyanus)
This pretty little thing, also known as Cornflower, is a noxious weed. Native to southern Europe, it is sometimes used in wildflower seed mixes.
“By far the worst weeds of the sagebrush steppe are the knapweeds of the genus Centaurea, in the sunflower family. Species of knapweeds combine a broad ecological tolerance with an unusual competitive ability. Plants sharing these “qualities” inevitably become noxious weeds.” -Ronald J. Taylor in Sagebrush Country: A Wildflower Sanctuary