No interactions present.
It looks like there are no other un-known Knapweeds on here so you may need to run a search to see the UK Greater Knapweed observations with one flower per stem.
I think that adding sp makes the difference, perhaps. I would imagine that there would be some unspecified Centaurea, if that was added on its own.
My Flickr photos...
C. triumfettii is certainly polycephalic, quite often. It might be worth a look...the bracts look similar.
It would be easier to give an ID if leaves were visible, too, and if an idea of height was given.
Thanks for trying so hard. Sorry, yes, failed to post an image with more leaves, which are much indented, which doesn't seem to be the case for triumfettii. The plant was quite tall from memory maybe 3foot and the extra image I plan to add supports this. I think it probably IS a subspecies of greater knapweed as images I can find of C scabiosa fristschii and C. scabiosa scabiosa DO show multiple flowerheads. See: http://luirig.altervista.org/naturaitaliana/viewpics.php?title=Centaurea... Could be either!
Nick Upton, naturalist and photographer.
Lat/Lng: 46.2731, 13.9337
Traditional hay meadow at 500m