A broad range of morphological variation is known to occur within the lichen-forming fungal genus Acarospora (Acarosporaceae, Ascomycota). In this study, we investigated the relationships of a number of interesting Acarospora collections from western North America using morphological, chemical and molecular sequence data. Our results revealed patterns of apparent convergence of some morphologies traditionally considered a single taxon, coupled with a striking range of morphological disparity within other lineages. Based on the results of this study, a species of lichen-forming fungi, Acarospora tintickiana sp. nov., is formally described as new to science, occurring on hard limestone substrates in the Great Basin of western North America. Furthermore, a number of additional candidate species are recognized and merit additional research before formal taxonomic recognition. This study highlights the importance of implementing an integrative taxonomic approach, incorporating a broad range of data, including molecular sequence data, for diagnosing evolutionarily independent species-level lineages in lichen-forming fungi.