Here's a look at the bracts of brown knapweed. Efforts to identify species of Centaurea invariably involve the bracts, which differ widely in color and fringe. In Flora of North America Keil and Ochsmann include a very good discussion of the efforts to deliniate Centaurea jacea. The plants have provided a persistent puzzle for botanists who want to make their chops by figuring out Centaurea. Now of course we can analyze the genome and get a final definitive answer, which is that this is a large and variable genus and pretty much includes all those plants people have separated in the past. A final answer! But what fun would that be? The very concise FNA item that leads us to believe in one species ends by saying, "We have chosen here to follow the traditional approach of recognizing three species . . ." And the beat goes on, and the beat goes on.