Bryologists are renowned for their upright moral character, bearing the strictest enquiry. However, should a bryologist see this moss, growing on a sun-kissed, crumbly, calcareous wall, even they may be guilty of employing an expletive. For not only is this rather a beautiful plant, the favourite moss of legendary Grimmiologist H. C. Greven, but it is also an extreme rarity in the British Isles, currently (2022) known from only two localities. So, what are we looking for?
Superficially, it resembles a very shaggy version of the very common Grimmia pulvinata. It is, though, eye-catchingly shaggy – the individual leaves are boat-shaped, widest above the middle and with long, silvery hair points. These are often flattened down and pointing in one direction, the plants forming grey patches ‘like mouse-skin’ according to H. N. Dixon, rather than the rounded cushions of G. pulvinata. A closer look reveals that the capsules, often present in good numbers, are sunk within the patch, not emerging on cygneous setae. The presence of peristome teeth should be checked and if further confirmation is needed, the short seta has a slight kink in it and is inserted asymmetrically at the capsule base. Should you ever be lucky enough to find this moss, please take only the smallest possible voucher for checking by the referee, as it really is a very rare plant.