Identification notes
It was a sad day for many bryologists when what we had grown up to call Barbula convoluta was renamed Streblotrichum convolutum. This is quite a mouthful for such a widespread plant, which is one of our commonest acrocarpous mosses, occurring on disturbed soil, paths, tracks, between paving stones and in numerous urban habitats. It avoids very acid habitats, and is a weedy species that is tolerant of eutrophication.
It is quite variable but in its typical form (var.convolutum) it forms tight cushions or low patches which attract attention because of the vivid bright green colour. The leaves are between 0.5mm and 1.5mm in length and are broadly lanceolate or more parallel-sided, tapering to an acute apex. The margins are usually recurved a little in the lower part of the leaf, and the nerve terminates just below a short apiculus which is often not actually formed from nerve tissue. The var. commutata is not such a bright green, because the cells are less papillose so they do not scatter the light so much. The leaf margins are undulate.
Capsules are not common, but it can fruit abundantly with yellow setae and sheathing, twisted perichaetial leaves.
It can be confused with other common acrocarps of similar habitats. Barbula unguiculata is usually larger with a more obtuse apex, recurved margins and a stout excurrent nerve. Didymodon species have more tapering leaves and are usually a darker colour. Pseudocrossidium hornschuchianum can have a similar colour and grows in similar places but the leaves are more triangular with recurved margins extending to the apex where the nerve extends into a sharp point, giving the plant a starry appearance.
Species varieties
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- Streblotrichum convolutum var. convolutum
- Streblotrichum convolutum var. commutatum
