Checklist of thallus-forming Laboulbeniomycetes from Belgium and the Netherlands, including Hesperomyces halyziae and Laboulbenia quarantenae spp. nov

In this paper we present an updated checklist of thallus-forming Laboulbeniomycetes (Ascomycota, Pezizomycotina), that is, the orders Herpomycetales and Laboulbeniales, from Belgium and the Netherlands. Two species are newly described based on morphology, molecular data (ITS, LSU ribosomal DNA) and ecology (host association). These areHesperomyces halyziaeonHalyzia sedecimguttata(Coleoptera, Coccinellidae) from both countries andLaboulbenia quarantenaeonBembidion biguttatum(Coleoptera, Carabidae) from Belgium. In addition, nine new country records are presented. For Belgium:Laboulbenia aubryionAmara aranea(Coleoptera, Carabidae) andRhachomyces spinosusonSyntomus foveatus(Coleoptera, Carabidae). For the Netherlands:Chitonomyces melanurusonLaccophilus minutus(Coleoptera, Dytiscidae),Euphoriomyces agathidiionAgathidium laevigatum(Coleoptera, Leiodidae),Laboulbenia fasciculataonOmophron limbatum(Coleoptera, Carabidae),Laboulbenia metabletionSyntomus foveatusandS. truncatellus(Coleoptera, Carabidae),Laboulbenia pseudomaseionPterostichus melanarius(Coleoptera, Carabidae),Rhachomyces canariensisonTrechus obtusus(Coleoptera, Carabidae), andStigmatomyces hydrelliaeonHydrellia albilabris(Diptera, Ephydridae). Finally, an identification key to 140 species of thallus-forming Laboulbeniomycetes in Belgium and the Netherlands is provided. Based on the combined data, we are able to identify mutual gaps that need to be filled as well as weigh the impact of chosen strategies (fieldwork, museum collections) and techniques in these neighboring countries. The aim of this work is to serve as a reference for studying Laboulbeniomycetes fungi in Europe.