Taxonomic investigation of <i>Abrothallus</i> (Abrothallales, Ascomycota) species associated with lichen genera <i>Ramalina</i> and <i>Bryoria</i> , including the description of a new species

The obligately lichenicolous genus Abrothallus consists of approximately 50 species, almost all of which are associated with lichens having foliose, fruticose, or pendulous thalli. This paper focuses on species that grow on strap lichens ( Ramalina ) providing new insights into their phylogenetic relationships and distribution. The three‐gene phylogeny, which includes one nuclear ribosomal (nrITS) and two protein‐coding genes (rpb2 and tef1‐α), shows that Abrothallus suecicus and A. ramalinae are only distantly related to each other. Abrothallus suecicus , characterized by four‐celled intact ascospores, forms a well‐supported clade with A. bryoriarum that grows on horsehair lichens ( Bryoria ). Within this clade, specimens associated with Ramalina exhibit significant morphological and genetic differentiation. Phylogenetic analyses, species delimitation using bGMYC, and morphometric data support the existence of five putative species, among which the true A . suecicus is growing on the apothecia of several non‐sorediate Ramalina. We describe Abrothallus farinaceae being exclusively known from Ramalina farinacea in Europe and North America. We also give a preliminary description for a singleton taxon with two‐celled ascospores that split in part‐spores, which is only distantly related to A. suecicus and A. ramalinae. Three Lichenoconium species included to root the phylogenetic tree appeared to be paraphyletic.