Identification notes

Tiny, beautiful and rather rare – Gymnostomum viridulum is definitely one of those ‘oooh’ mosses! At only a millimetre or two in height, even the most eagle-eyed bryologist is unlikely to spot it unless they are down on their knees and peering very closely at the substrate. Fortunately, it is a gregarious species and although individual plants are minute, dense patches can catch the eye.

This moss is always a vivid yellow-green colour, similar to e.g. Streblotrichum convolutum and Pseudocrossidium hornschuchianum, with which it sometimes grows. However, G. viridulum is far smaller than either species. Although the obtuse leaf apex that is characteristic of this species is readily seen with a hand-lens, a microscope is more suitable for confirming its plane (not recurved) leaf margins and the presence of distinctive axillary gemmae.

Distribution in Great Britain and Ireland

Of our three species of Gymnostomum, G. viridulum prefers the warmest and driest habitats and is the only one likely to be found in seasonally parched calcareous grassland, on skeletal soils overlying old walls or lime mortar in masonry.