This little moss caused quite a stir when molecular analysis of a population collected from a Yorkshire reservoir confirmed it new to Europe (as Ephemerella readeri). Its publication, in 2010, came too late for inclusion in the second edition of Smith’s moss flora or the first edition of the Field Guide and so many bryologists are probably unaware of it.
It’s a species of barish silt on reservoir margins and can sometimes grow in great profusion when conditions are favourable. There is growing anecdotal evidence that it favours lower reservoir margins that are only exposed during exceptionally dry summers. Like other species of Physcomitrium, it is an opportunist with a very short life-cycle. In appearance, it most closely resembles the common P. patens, but it is a smaller plant and, when capsules are mature, they differ in being dark brown to black. They are borne on a short seta, which raises them slightly above the plant. Its leaves are particularly distinctive: they are widest above the middle and so look spathulate or obovate with a short apiculus. Margins have very large and obvious teeth above.