Taxonomic review of Epeorus s. l. Eaton, 1881 (Ephemeroptera: Heptageniidae) in Sapporo City and adjacent areas, Hokkaido, Japan.

Three species within the genus Epeorus s. l. Eaton, viz., Epeorus latifolium Uéno, 1928, E. L-nigrum Matsumura, 1931, and E. uenoi (Matsumura, 1933), whose types were collected from Sapporo City, Japan, and neighboring areas, have been confused for a long time. In this study, intensive field sampling and investigation of museum specimens revealed E. latifolium and E. L-nigrum are indeed distinct species, while E. uenoi is a synonym of E. latifolium. Thus, this study partially resolves the taxonomic confusion surrounding Japanese E. latifolium-like species. However, numerous closely related species in Northeast Asia remain challenging to delineate. A critical factor in this taxonomic ambiguity is the definition of subgenus Belovius Tshernova, 1981, as the description of its type species, E. latifolium, was based on a misidentified specimen. Additionally, this study presents morphological features and DNA sequence data for three other related species from the same areas, viz., E. curvatulus Matsumura, 1931; E. aesculus Imanishi, 1934; and E. nipponicus (Uéno, 1931). The subgeneric classification of each species is evaluated following Kluge's (2004) system, with E. L-nigrum newly assigned to the subgenus Belovius and E. curvatulus to the subgenus Caucasiron Kluge, 1997.