Taxonomic complexity in the genus Merodon Meigen, 1803 (Diptera, Syrphidae)

The genus Meigen, 1803 is distributed across the Palaearctic and Afrotropical Regions. The present work summarizes the knowledge from recent taxonomic and systematic revisions and includes an identification key for the five monophyletic lineages (namely , , , and ), 24 species groups, two species subgroups and 10 unplaced species, along with diagnosis and illustrations. A list of 234 taxa, including 194 described and 40 undescribed species, is appended. Most of the species are distributed in the Palaearctic (209 taxa, 181 described), while 27 species (14 described) are known from the Afrotropical Region. Three lineages ( , and ) are present in the Afrotropical Region, as well as in the Palaearctic. The Afrotropical species group of the lineage and the species group of the lineage are endemic to the Afrotropical Region, and all other species groups belong to the Palaearctic fauna. The lineage contains six species groups ( , , , , and ) and two unplaced taxa. The lineage includes five species groups ( , , , and ). The lineage is divided into 10 species groups ( , , , , , , , , and ) and eight unplaced taxa. The lineage contains two species groups: the Afrotropical group, with the and subgroups plus the species Curran, 1939, and the Palaearctic species group. The lineage consists of the species group plus the species Fabricius, 1794.