According to Jeannel (1940), Camedula and Callitropa, that occupy Central America and southern United States, belong to a single phyletic line and are phylogenetically related to South American Castrida from which they differ in the chaetotaxy and in particular for having lost the brush on the male's mesotibiae. In the same lineage would also have evoluted the species of wingless mountain Calosoma, collected in the sub genera Carabomimus and Calopachys, that are limited to Mexico.
Inside this phyletic line, the species belonging to the subgenus Callitropa are characterized by the pronotum with arcuate sides, well developed rear lobes, and widely rounded basal angles. The humerus of elytra is smooth, without teeth (except C. haydeni).
The subgenus Callitropa (which, according to Jeannel, was a distinct genus) includes winged, brachypterous and apterous species, living in United States and Mexico. The winged species are externum, macrum and protractum, that previously formed the subgenus Callitropa s. str. palmeri is a brachypterous species that is exclusive to Isla Guadalupe, off the coast of Baja California, and that was previously attributed to a separate subgenus (Paracalosoma). The apterous species, exclusive of Mexico, are: anthracinum, atrovirens, laeve, porosifrons, viridisulcatum, collected by Jeannel in the subgenus Blaptosoma, and haydeni that Jeannel included in Camedula because of the character of serrate elytral margin near the humerus.