Bryophytes, far from being the infection-impervious organisms they are often misconceived to be, are colonized by a diversity of fungal parasites, saprobes and commensals, at least some of which likely recapitulate plant-fungal interactions in the first land plants. These fungi, the vast majority of described species of which belong to the phylum Ascomycota, and many of which are obligate parasites and host-species specific, have been deemed “bryophilous”. The leafy liverwort genus Gymnomitrion Corda (Jungermanniales, Gymnomitriaceae) is a predominately northern hemisphere genus that grows on exposed or somewhat sheltered rock surfaces, on well-drained tundra and among boulders in coastal and mountainous areas, and consists of six species in North America. The genus is known to be a common host for bryophilous ascomycetes, most of which have been documented on host plant collections from localities in Europe. Bryophyte specimens preserved in herbarium collections, at present still largely uninvestigated for the presence of bryophilous fungi, have high potential to reveal new species and new occurrences, at least for those ascomycete taxa which are desiccation and decay resistant (mainly Classes Eurotiomycetes and Dothideomycetes). The present study represents the first concerted effort to document bryophilous fungi from herbarium specimens of Gymnomitrion in North America. With the aim of increasing understanding of the variety and global distribution of different fungal taxa parasitic or epiphytic on Gymnomitrion, we screened over 100 specimens from multiple herbaria (mainly from ALA and OSC), mostly collected from western North America (the Pacific Northwest, Alaska and the Aleutian Islands) but also from Eurasia (Europe and the Russian Far-East).  Our findings revealed a higher-than-expected number of parasitic fruiting-body forming ascomycete taxa on Gymnomitrion. These included first records of previously known bryophilous taxa for North America; new occurrences of both lichenized and non-lichenized species as epiphytes and parasites, respectively, on the host genus and/or species; at least one new combination; and possibly one or more species new to science, including a true bryoparasitic fungus (Pleosphaeria sp). In addition to contributing to basic knowledge of these organisms, our findings reaffirm the value of herbarium collections as a tool for filling gaps in knowledge of bryophilous ascomycete biodiversity and biogeography. We hope the study will serve to both highlight the need for and encourage similar investigations seeking to further expand understanding of this fascinating but neglected field representing an intersection between bryology, lichenology and mycology, and conducted by only a handful of researchers worldwide up to the present.