Question: I identified the flower on the left as Centaurea montana (Bachelors-button) several years ago but now am not so sure. …
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Question
I identified the flower on the left as Centaurea montana (Bachelors-button) several years ago but now am not so sure. The flower on the right is surely Centaurea montana, and they look very different. The individual flowers looks more like those of a blue "ragged-robin".
Answer
Dear DavidBlair, those are two different species. The first (more compact) image may be Centaurea cyanus (garden knapweed, sometimes called bachelor's-buttons). The second image is likely Centaurea montana (mountain knapweed), but I can't see the involucral bracts around the base of the flowers to help you know that with confidence. If you can take a side-view image I can assist you more.
