Identification notes
This is a plant which likes sheltered, well-drained locations, such as the sides of walls, the bases of shaded hedgebanks, roadside banks, edges of paths…just the sort of places where bryologists like to poke about. It looks a little like B. capillare, which is helpful, as it starts you looking in the right area for an identification. It shares with that species the leaf shape – widest above the middle. However, the nerve is not so excurrent and the leaves when dry, though shrunken and curled, do not form the characteristic twisted spirals familiar to every bryologist. The most striking feature of this moss is the very well-defined, multi-stratose, thickened leaf border, quite spectacular in section under the microscope and readily visible with the hand lens.
Not usually mentioned, but a trap for the unwary, is that Tortula subulata grows in many similar habitats: well-drained soils, roadsides, woodland banks… it is very variable in its leaf shape and also has a noticeably differentiated leaf margin under the hand lens. However, this species is usually fertile, in contrast to B. donianum, and with a really good hand lens and a bright background such as a sunlit sky, the individual elongated cells of the Bryum can be seen, whilst the quadrate, papillose cells of the Tortula are not really discernible. If in doubt, the microscope renders the difference immediately obvious.
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