The Caloplaca crenulatella species complex; its intricate taxonomy and description of a new species

The Caloplaca crenulatella species complex is monophyletic, based on analysis of ITS nrDNA sequences. It is characterized mainly by its ascospores and a simplified thallus. Caloplaca aquensis, C. borysthenica, C. interfulgens, C. lactea, C. marmorata and C. tominii represent well-defined monophyletic lineages within it. Caloplaca diffusa, described here as a new species, is a well-supported lineage with a distinctive phenotype. Caloplaca crenulatella s. lat. and C. ferrarii s. lat. are heterogeneous taxa appearing in four and two places respectively within our tree. Caloplaca ochracea also belongs to the group, although it has different ascospore characters. Caloplaca gyalolechiaeformis and C. pseudo-citrina are later synonyms of C. tominii. Arctic and North American sorediate specimens morphologically very close to C. tominii represent a separate lineage recently recognized as C. erichansenii. The North American Caloplaca nashii has a C. crenulatella-like phenotype but does not belong to the C. crenulatella complex. The identities of Caloplaca lacteoides and Caloplaca epigaea are not clear, but the latter may be a terricolous ecotype of one of the entities within C. crenulatella s. lat. A key to the European species of the group is provided.