Identification notes
The deft-of-hand bryologist will be able to confirm this species in the field by picking off stem leaves to see the obvious auricles formed by enlarged alar cells. However, leaves often overlap each other and obscure the auricles so for some it is a character best confirmed microscopically. Do not automatically assume that a Brachythecium growing in a damp place is going to be B. rivulare – B. rutabulum is surprisingly tolerant of damp ground, although it usually avoids places where it is regularly inundated by running water.
Shoots of B. rivulare have a certain look not shared by close relatives. Shoots are often arched, pale and glossy-looking and leaves are quite appressed so look smooth. Often, the shoot tips look distinctly pointed, a little like Calliergonella cuspidata.
When growing in riparian habitats, such as on rocks and boulders that are sometimes submerged, B. rivulare is a member of a community of species that indicates neutral to base-rich water. It becomes be scarce in base-poor water of low pH where it is usually replaced by Sciuro-hypnum plumosum.
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