Identification notes
When you find this species for the first time, you will probably doubt that it is a Grimmia. Its neat-looking cushions with strap-like leaves with often cucullate tips resemble a darkly coloured Trichostomum crispulum. But, Grimmia atrata is a rare plant of acid soils with high concentrations of copper and other heavy metals so the two species will rarely if ever coexist.
When you put it under the microscope, its affinity with Grimmia becomes clearer as the mid-leaf cells have sinuose, thickened walls. It is one of only two British Grimmia species that always lack a hair-point (although a number of others can be muticous); the other is the even rarer G. unicolor. At least this makes it an easy species to take through the Grimmia key.
Read the Field Guide account
