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Arthonia frostiicola and A. galligena are described as new to science based on collections from mountainous regions of southeastern North America. Arthonia frostiicola infects the saxicolous lichen Dirinaria frostii, producing emarginate black apothecia which erupt from within the host thallus. It is characterized by a dark hypothecium and 1-septate, obovoid ascospores which turn brownish and verruculose in age. It is known from five collections made in the southern Appalachian Mountains and Ozark Mountains in southeastern North America. Arthonia galligena produces galls in the thallus and apothecia of the corticolous lichens Lecanora masana and L. rugosella, and is apparently endemic to the high elevations of the southern Appalachian Mountains. It is characterized by a variably pigmented, pale to red-brown hypothecium and 2-septate, macrocephalic ascospores which turn brownish and verruculose in age. Keys to the species of Arthonia on Caliciales and Lecanoraceae are provided. [ABSTRACT FROM AUTHOR]

Species of lichen-forming fungi (LFF) display an array of geographical distribution patterns. Among the broadly distributed lichen-forming fungal species, the degree of reproductive isolation and genetic substructure among populations varies widely, in some cases masking unrecognized diversity or meaningful biogeographical patterns. Lecidea atrobrunnea (Raymond ex Lam. & DC.) Schaer. s. lat. (Lecideaceae) is a widespread species complex that has been studied for over two centuries since its initial description. The diversity of the L. atrobrunnea group is highest in western North America, where a dizzying array of morphologies and chemistry can occur at local scales. Here we investigate whether the assumed cosmopolitan distribution of L. atrobrunnea s. lat. is an artifact of taxonomic limitations and masks biogeographical patterns in this species complex. To address these questions, we compiled sequence data from the standard fungal barcoding marker (ITS) for over 100 specimens within this complex, in addition to genome-scale data from a subset of these representing over 1600 single-copy nuclear genes spanning over 3 Mb of the genome. Our study corroborates the perspective that the morphologically and chemically variable Lecidea atrobrunnea group reflects a complex of distinct species-level lineages, with 42–83 candidate species inferred from the ITS region and high levels of diversity inferred from a subset of specimens using genome-scale data. However, both phenotype- and molecular-based species boundaries remained unsettled, with the most common nominal taxa recovered as highly polyphyletic and with conflict among different molecular species delimitation approaches. Our study also highlights the potential for geographically restricted species, with fascinating biogeographical patterns, challenging, in part, the assumed cosmopolitan distribution of L. atrobrunnea s. lat. This study provides valuable direction for future research that will be crucial in understanding diversification and establishing a robust taxonomy for this well-known species complex. [ABSTRACT FROM AUTHOR]