Phylogenetic review of the millipede genus Chamberlin, 1949 (Polydesmida, Xystodesmidae).

The millipede genus Chamberlin, 1949 is a monospecific taxon, with the type species (Bollman, 1889). The last revision of the genus was made by Hoffman (1960) where he established three subspecies. Here we used molecular phylogenetics to assess the genus and evaluate whether it is a monophyletic group, and if the subspecies are each monophyletic. We included material from literature records and three natural history collections. Newly collected samples were obtained through a citizen science project. Morphological characters underlying subspecies groups-the shape of the paranota, body size, and coloration-were evaluated. A molecular phylogeny of the genus was estimated based on DNA sequences for seven gene loci, and a species delimitation analysis was used to evaluate the status of the subspecies. The documented geographical range of in the United States was expanded to include a newly reported state record (Virginia) and about 160 new localities compared to the previously known range. Morphological characters, which included the shape of the paranota and body size that had been historically used to establish subspecies, showed clinal variation with a direct relationship with geographical distribution and elevation, but not with phylogeny. Coloration was highly variable and did not accord with geography or phylogeny. The phylogeny recovered as a monophyletic lineage, and the species delimitation test supported the existence of a single species. The subspecies (Chamberlin, 1939) and Hoffman, 1960 have been synonymized with . The molecular and morphological evidence showed that is a monospecific genus with the sole species, , being geographically widespread and highly variable in its morphology.