The genus Asydates Casey (Coleoptera: Melyridae) is revised, containing three species from Arizona and California: A. explanatus Casey; A. inyoensis (Blaisdell), new combination; and A. rufiuentris Casey. The monotypic genus Pseudasydates Blaisdell is placed in synonymy with Asydates Casey, syn. nov., and Asydates puncticeps Blaisdell is placed in synonymy with Asydates explanatus Casey, syn. nov. A key separating adults of Asydates species is provided, and the results of a computerized cladistic analysis of Asydates species are presented. GIS mapping of Asydates species distributions indicates that these species are nearly allopatric, with A. explanatus found in the lower Colorado River basin and adjacent deserts, A. inyoensis restricted to the Inyo and White Mountains, and A. rufiuentris found in the coastal plain and coastal mountains near Santa Barbara. Geographic hypotheses of character evolution within Asydates are developed by combining the results of cladistic analysis and GIS mapping
