| Summary: | Herein, we revise the Rhizocarpon badioatrum species complex in the Nordic countries using molecular phylogenetics combined with morphological/anatomical and chemical data. Bayesian and Maximum Likelihood phylogenetic analyses of the nuclear ribosomal internal transcribed spacer (ITS, the fungal DNA barcode) reveals four strongly supported clades within the R. badioatrum species complex. Based on our assessment of the multiple sources of data included, we recognize R. badioatrum var. badioatrum and var. vulgare at the species level and describe the latter as the new species R. vulgare. Rhizocarpon vulgare receives support also from a phylogeny based on mitochondrial ribosomal small subunit (mtSSU). Rhizocarpon cinereonigrum is the phylogenetic sister species of R. vulgare in both the ITS and mtSSU trees. Rhizocarpon sinense is reported as new to Europe with specimens collected from Iceland and Norway. The secondary chemistry is shown to be largely diagnostic for the species: R. badioatrum is usually acid deficient, R. vulgare contains diffractaic acid, and R. sinense contains gyrophoric acid. However, the concept of R. cinereonigrum, which was previously based on the presence of stictic acid, is shown to be ambiguous because that compound may also occur in R. badioatrum. Lectotypes are designated for Lecidea atrobadia, Rhizocarpon badioatrum, R. rivulare, R. sinense.
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