On rock in the Plym
No interactions present.
When I get home I'll describe it properly and catch up with the dozens of others mosses I've got to try and key out...
Looking at it with a hand lens, I'm not sure at all: Stem 7mm, leaves 1-1.5mm, mostly black, with a few leaves at the tip yellow green, and they all have a dark, pointy curvy extension.
That doesn't sound like Racomitrium aciculare, does it?
R aciculare has blunt leaves. Any chance of a close up?
Now back home, I've just tried keying it out and have tentatively got to Andreaea rothii. Is that possible?
Yes, I think you're right.
Lat/Lng: 50.4949, -3.9656
OS grid ref: SX606679