With its thickened leaf border, reddish pigments and double marginal teeth, this is unmistakably a Mnium. Mnium hornum is a calcifuge, so it’s always worth checking any medium-sized Mnium plants with clearly decurrent leaf bases growing in a base-rich place for M. marginatum, the most likely of several similar-looking uncommon species (M. thomsonii and M. ambiguum are more usually montane species).
Read the Field Guide account
Most likely to be confused with other, rarer species of Mnium.
