<i>Cladonia rubrotincta</i> , a new species distinct from <i>C. norvegica</i>

Abstract Cladonia norvegica was originally described from Norway based on different morphological and chemical characters distinguishing the species from C. coniocraea. Shortly after its description, material containing red spots on the thallus was reported from different parts of the world, but the taxonomic status of this form remained unclear. In this study, we investigated the morphological, chemical and genetic differences between the spotless form of C. norvegica and the red-spotted material. Phylogenetic analyses of mycobiont DNA (ITS rDNA, mtSSU, EF-1α) revealed that red-spotted specimens form a well-supported monophyletic clade, distinct from the spotless form of C. norvegica. We therefore describe red-spotted material as a new species, C. rubrotincta , with the type from Norway and we genetically and morphologically confirm occurrences from Austria, Czechia, Estonia, Great Britain and western Canada. The identity of the red pigment was confirmed to be a rhodocladonic acid by HPLC and LC-HRMS. Specimens with red spots exhibit consistently smaller and more irregularly shaped podetia. Additionally, our analysis of photobionts indicated that both species share a similar pool of Asterochloris symbionts. This study underscores the importance of integrating molecular, chemical, and morphological data in lichen taxonomy and provides insights into the distribution and ecological preferences of C. rubrotincta and C. norvegica.