I've been going through another interesting batch of specimens from Cornwall and come across this - http://fungi.myspecies.info/all-fungi/pyrenula-sp-p2285. It's not lichenized and occurs on dead (I think) stems of Rubus, but the asci and ascospores are so distinctive I can't think of where else to place it. I haven't seen material of Pyrenula coryli which is also supposed to be non-lichenized, but that has 3-septate ascospores rather than the 1-septate ones in this collection, and obviously the substrate is different. It doesn't seem to fit with Acrocordiella which was once considered close to Pyrenula, but is known now to be rather distantly related.
I'm often wrong (sometimes very wrong!) and would much appreciate it if someone has seen this before and can give it a better name.

Best wishes
Paul