Integrative taxonomy and genus delimitation in the <i>Rhizocarpaceae</i> (lichenized <i>Ascomycota</i> )

The <i>Rhizocarpaceae</i>, a family of lichenized fungi within the <i>Ascomycota</i>, comprises approximately 160 species within five genera: <i>Catolechia</i>, <i>Epilichen</i>, <i>Haugania</i>, <i>Poeltinula</i>, and <i>Rhizocarpon</i>. <i>Rhizocarpon</i> 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 <i>Rhizocarpon</i> paraphyletic. This study aims to elucidate the phylogenetic relationships and clarify genus delimitation within the <i>Rhizocarpaceae</i> 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 <i>Rhizocarpaceae</i> 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 <i>Rhizocarpaceae</i>, highlighting the inadequacy of traditional taxonomic markers alone to infer robust phylogenetic affiliations. We advocate for new circumscriptions of <i>Catolechia</i>, <i>Poeltinula</i>, and <i>Rhizocarpon</i> based on the molecular phylogeny and propose synonymizing <i>Epilichen</i> with <i>Catolechia</i>, the transfer of the species in the <i>R. hochstetteri</i> complex to <i>Poeltinula</i>, and the resurrection of <i>Rehmia</i>. 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 <i>Rhizocarpaceae</i>, augmenting our understanding of their diversity and evolutionary dynamics. <b>Citation:</b> Möller EJ, Timdal E, Haugan R, Bendiksby M (2025). Integrative taxonomy and genus delimitation in the <i>Rhizocarpaceae</i> (lichenized <i>Ascomycota</i>). <i>Fungal Systematics and Evolution</i> <b>16</b>: 215-231. doi: 10.3114/fuse.2025.16.12.