Identification notes
This riverside moss is still local in its distribution, mainly restricted to a few rivers in the South and West of England, but can be abundant where it grows. When first encountered, covered with silt on a stony bank or tree next to the river, it can look like some other riparian mosses with dried and curled up leaves, such as Dialytrichia mucronata or even Cinclidotus fontinaloides. On wetting up, examination with a hand lens reveals a tongue-shaped leaf with a thickened border and mucronate leaf tip, very similar to D. mucronata in fact. However, the most striking thing is that the moss seems to have disintegrated into a rather untidy state. The leaves have split apart, many losing their tips, some with only the midrib left. Interestingly the splits occur not in a random fashion but mainly either parallel or perpendicular to the leaf axis, resulting in rectangular leaf fragments. D. mucronata leaves also split sometimes, but not in such a neat manner, the lines of breakage often curved or oblique, resulting in irregularly shaped fragments. Under the microscope the structure of the leaf margin transverse section is diagnostic. In addition, on viewing the whole flattened leaf, the leaf margin appears markedly crenate, unlike the smoother border of D. mucronata. This latter feature can be seen in the field with a hand lens and a good eye.
