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Description

<b>Abstract</b><br/>

<em><span lang="EN-GB">Bryoria</span></em><span lang="EN-GB"> (Parmeliaceae, Ascomycota) is one of the dominant genera of hair lichens in western North America and is characteristic of high-elevation conifer forest ecosystems. In areas where <em>Bryoria</em> is abundant, it is common to find thalli in which the thalline filaments become conglutinated, forming brittle dead zones. After sampling <em>Bryoria</em> <em>thalli</em> across western Canada and the northwestern United States at different times of the year, we found this dieback phenomenon is associated with the winter growth of a mold-forming basidiomycete. We report that this fungus belongs to <em>Athelia</em> (Atheliaceae, Basidiomycota) a genus known to contain lichen pathogens, most notably <em>A. arachnoidea</em>. By sequencing a combination of genetic markers – nuc rDNA ITS1-5.8S-ITS2 (ITS), partial nuc 28S rDNA (28S), and partial translation elongation factor 1-α (<em>TEF1</em>) – paired with morphometric analyses, we reveal the involvement of at least three additional lineages of lichen-associated <em>Athelia</em> and describe one as a new species, <em>Athelia abscondita</em>. <em>A. abscondita</em> is morphologically distinguished from other <em>Athelia</em> species by its basidia and basidiospores, was found to frequently infect members of <em>Bryoria</em> sect. <em>Implexae</em>, and was occasionally on other foliose and fruticose species within Parmeliaceae.</span></p>