Identification notes
This rather rare Mnium is typically a species of montane crags on ledges where the rock is usually distinctly calcareous and base-rich. It grows with a suite of other vascular and bryophyte calcicoles that would not normally be associated with Mnium hornum, a calcifuge.
In the field, it often looks very red (stem, leaf border, nerve…) and is quite small. The conspicuously decurrent leaf base is easily seen with a x 20 lens and invites further microscopic investigation. The species it is most likely to be confused with in calcareous situations is M. marginatum.
