Cylindric Beard-moss. It used to be called Barbula cylindrica.
I’m going out on a limb with this one – these little mosses are difficult for me. But until I know better, I’ve decided that the little orangey-brown moss on top of the wall is Didymodon insulanis.
From what I’ve read, this moss also comes in green, but it’s the orange/olive patches which have caught my eye. “Ginger”, I’d call it.
Close up, it looks quite different wet and dry. When it’s wet, you can see the starfish spread of the leaves, which the book describes as a spiral.
When dry, the leaves are curled and twisted.
Even at a distance, it looks different when wet (left) or dry (right).
Mr Watson says it grows in rather loose, ill-defined tufts on soil, which makes me hesitate a bit in going for Didymodon insulanus. But under the microscope it all matches the illustrations in his book, and the BSS Guide (“the book”) says it comes in loose tufts or patches while stone walls are included in the habitat list. So my tight little wall patches seem to be covered by this.
I’m going to keep an eye out for the same moss growing on soil, which may be more typical.
By November, the same clump had turned bright green.
I found some pictures taken at Ben Lawers in 2019, which I had identified as Didymodon insulanus. But I can’t remember how thoroughly I checked, and D. insulanus is very like D. vinealis. The pictures include some capsules, which the books say are rare/very rare for both D. insulanus and D. vinealis…however, I’m going to add them in here for the time being at least. Lovely twisted filiforme peristome teeth.