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The new genus Atla forms a well-supported dade in a molecular phylogeny based on the ITS 1-5.8S-ITS2 and LSU regions of the nuclear ribosomal DNA. The genus has a crustose thallus, a hamathecium at maturity without hyphal elements except for pseudoparaphyses remaining at the ostiolum, and large, muriform spores. Ada wheldonii was previously referred to Polyblastia. Three new species, A. alpina (the type of the new genus), A. palicei and A. praetermissa, are included in the genus and described here as new to science. They were found on calcareous rocks and soil in Northern Scandinavia; A. alpina also occurs in Central Europe, and A. wheldonii likewise in Central Europe, the Pyrenées and in the British Isles. An identification key to the species and a revision of the genus are also provided. [ABSTRACT FROM AUTHOR]