Integrative taxonomy and genus delimitation in the Rhizocarpaceae (lichenized Ascomycota)

The Rhizocarpaceae, a family of lichenized fungi within the Ascomycota, comprises approximately 160 species within five genera: Catolechia, Epilichen, Haugania, Poeltinula, and Rhizocarpon. Rhizocarpon is the most species-rich, with about 150 species predominantly inhabiting siliceous rock in boreal and arctic-alpine environments. Molecular phylogenetic studies have revealed that current taxonomy, heavily reliant on morphology, chemistry, and life strategies, renders Rhizocarpon paraphyletic. This study aims to elucidate the phylogenetic relationships and clarify genus delimitation within the Rhizocarpaceae using an integrative taxonomic approach that combines three genetic markers and a diversity of taxa covering the morphological, chemical, and ecological spectrum of the family. Our comprehensive sampling includes 50 species across the Rhizocarpaceae collected from diverse geographical locations and ecological settings. Our phylogenetic hypothesis is based on a concatenated dataset of two nuclear (ITS and MCM7) and one mitochondrial (mtSSU) genetic marker. Ascospore characteristics and thallus pigmentation alongside secondary metabolite profiles were mapped onto this DNA-based evolutionary framework. Our results underscore significant refinements in the classification of the Rhizocarpaceae, highlighting the inadequacy of traditional taxonomic markers alone to infer robust phylogenetic affiliations. We advocate for new circumscriptions of Catolechia, Poeltinula, and Rhizocarpon based on the molecular phylogeny and propose synonymizing Epilichen with Catolechia, the transfer of the species in the R. hochstetteri complex to Poeltinula, and the resurrection of Rehmia. We hence propose 24 new combinations and three typifications. Collectively, this study sets the groundwork for future research and stability in the systematics of the Rhizocarpaceae, augmenting our understanding of their diversity and evolutionary dynamics. Citation: Möller EJ, Timdal E, Haugan R, Bendiksby M (2025). Integrative taxonomy and genus delimitation in the Rhizocarpaceae (lichenized Ascomycota). Fungal Systematics and Evolution 16: 215-231. doi: 10.3114/fuse.2025.16.12.