The genus Baetis includes three groups of subgenera: Nigrobaetis group (with subgenera Nigrobaetis, Fallceon, Caribaetis, and Americabaetis), Labiobaetis group (with subgenera Labiobaetis and Acerpenna), and Baetis group (with subgenera Baetis Acentrella and Baetiella). Characters of these groups and characters of subgenera of the Nigrobaetis; the new synonymy is discussed. A key to all known nymphs of the subgenus Nigrobaetis of the world fauna (22 species) and a key to male imagines of 10 Palearctic species examined by the authors are given. -from Journal summary