Identification notes
Didymodon can be a tricky genus with a lot of quite similar species, confusing many bryologists for years. D. luridus is one of the easier species to identify, with characteristically wide-based, almost triangular leaves and a rounded or blunt-tipped apex. However forms occur with narrower leaves which can easily be confused with D. nicholsonii.
It is always worth looking at leaf sections of Didymodon spp. if you have a compound microscope. In the case of D. luridus and D. nicholsonii, the costa sections look quite different (see images and refer to Tom Blockeel’s recent article, linked below.
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