I put the '?' in the title to cover myself in case it's not a Jungermannia.
This is another one from Merthyr Common last week. It was growing as a dense patch on a wet, shady rock face (sandstone/shale, fairly base rich).
I thought this might be J. pumila. This size is about right (stems 1.5-2mm across) and it is not aromatic (verified by Liz who has a better sense of smell than me). However, I can't find any fertile material, so perhaps it is not possible to confirm it is this species and not J. atrovirens, or something else entirely.
Comments welcome, thanks.