A long tradition of separate Nearctic and Palaearctic taxonomic studies of the diverse aleocharine rove beetles (Coleoptera: Staphylinidae) has obscured the recognition of Holarctic species and detection of adventive species in both regions. Recently, integrated study of the two regions through detailed morphological comparisons and development of an authoritatively identified DNA barcode reference library has revealed the degree to which these two aleocharine faunas are interconnected, both naturally and through human activity. Here this approach is adopted to recognize new species, reveal Holarctic species, and recognize adventive species in both North America and Europe. The following new species are described: Isoglossa triangularis Klimaszewski, Brunke & Pentinsaari, sp. nov. from British Columbia; Gnypeta impressicollis Klimaszewski, Brunke & Pentinsaari, sp. nov., from Ontario, Maryland and North Carolina; Aloconota pseudogregaria Klimaszewski, Brunke & Pentinsaari, sp. nov., from Ontario and Virginia; and Philhygra pseudolaevicollis Klimaszewski, Brunke & Pentinsaari, sp. nov. from eastern Canada. Dasygnypeta velata and Philhygra angusticauda are revealed to be Holarctic species, resulting in the following synonymies: Dasygnypeta velata (Erichson, 1839) = Gnypeta minuta Klimaszewski & Webster, 2008, syn. nov. and Philhygra angusticauda (Bernhauer, 1909) = Atheta (Philhygra) pinegensis Muona, 1983, syn. nov. The Nearctic species Hylota ochracea (and genus Hylota), Thecturota tenuissima, and Trichiusa robustula are newly reported from the Palaearctic region as adventive, resulting in the following synonymies: Hylota ochracea Casey, 1906 = Stichoglossa (Dexiogyia) forticornis Strand, 1939, syn. nov.; Thecturota tenuissima Casey, 1893 = Atheta marchii Dodero, 1922, syn. nov.; and Trichiusa robustula Casey, 1893 = T. immigrata Lohse, 1984, syn. nov. The Palaearctic species Amarochara forticornis, Anomognathus cuspidatus, Oligota pumilio, and Parocyusa rubicunda are newly confirmed from the Nearctic region as adventive, resulting in the following synonymies: Parocyusa rubicunda (Erichson, 1837) = Chilopora americana Casey, 1906, syn. nov. and Anomognathus cuspidatus (Erichson, 1839) = Thectura americana Casey, 1893, syn. nov. The genus Dasygnypeta, sensu nov. is newly reported from North America, Paradilacra is newly reported from eastern North America, and Haploglossa is newly reported from Canada, resulting in the following synonymy: Paradilacra densissima (Bernhauer, 1909) = Gnypeta saccharina Klimaszewski & Webster, 2008, syn. nov. Native Cyphea wallisi is newly reported from across Canada and C. curtula is removed from the Nearctic fauna. The status of both Gyrophaena affinis and Homalota plana is uncertain but these species are no longer considered to be adventive in North America. Three new combinations are proposed: Dasygnypeta baranowskii (Klimaszewski, 2020) and D. nigrella (LeConte, 1863) (both from Gnypeta) and Mocyta scopula (Casey, 1893) (from Acrotona). Dolosota Casey, 1910, syn. nov. (type species Eurypronota scopula Casey), currently a subgenus of Acrotona, is therefore synonymized with Mocyta Mulsant & Rey, 1874. Additionally, four new Canadian records and 18 new provincial and state records are reported.
Keywords: Canada; DNA barcodes; North America; United States; faunistics; morphology; rove beetles.