Greater knapweed

I love this form of greater knapweed with its long rays that are mostly white. It occurs quite frequently at the nature reserve, in the ex-arable fields that were reseeded. The seed was all of native origin, from known harvest sites, so I wonder if we just struck lucky with the amount of this very beautiful form. I think I've seen butterflies happily nectaring on it, but I should probably check a bit more systematically whether it is chosen as often as the more typical deep purple and less extremely rayed form.