These are all photos of flowerheads from group of same plant.
No interactions present.
Thanks for the agreements everyone - does anyone know if this is an unusual spot for this part of Norfolk? I hadn't seen S. arvensis before - this was one small group on a field footpath edge that was ploughed out in autumn last year. I haven't seen it anywhere else since!
Lat/Lng: 52.7992, 1.437
OS grid ref: TG317279
Only seen here in one spot, on edge of field footpath in 2010- it didn't reappear this summer. Have not seen it anywhere else since.