You may have realised from my original wording that I was not particularly confident with my tentative ID of this one.
Sorry, taken with my old box brownie, so pic is very heavily cropped, and the only one I have. However, enlarged as far as poss, which shows what you mean to anyone who does not know the apiculus.
This leads me to ask, what is it then, as I've discarded all the Potanthus?