Temperate forests are hotspots of biodiversity and some of the most threatened ecosystems of Mesoamerica. Understanding the biogeographical patterns of species inhabiting these forests is a crucial part of designing effective conservation strategies. Yumtaax Boucher is a genus from the family Passalidae distributed in the Temperate Serrias of Mexico with a high degree of endemism. Species in the genus have had an unstable taxonomic history, and a phylogenetic approach to understand species delimitations and relationships between these species is necessary. This study reconstructed the molecular phylogeny of 6 operational taxonomic units (OTUs) in the genus, using parsimony and Bayesian analysis of DNA sequence data from the nuclear gene region 28S, and the mitochondrial gene regions 12S and Cytochrome Oxidase I (CO1). Analyses recovered two well supported Yumtaax clades (Y. laticornis clade and Y. imbellis clade), but not a monophyletic Yumtaax. The number of species in the genus was increased from six to nine species due to discovery of two separate, evolutionary lineages (=species) of Yumtaax recticornis and the presence of two undescribed morphotypes that are included within the well supported Yumtaax clades. Gene performance for supported taxonomic groups (=lineages, clades) was measured and, based on these data, it is possible to test species delimitation within the family Passalidae using 12S and CO1 mitochondrial sequences. Further studies need to be conducted to resolve generic level relationships. Species of Yumtaax are distributed in four forest types (oak forest, pine forest, pine-oak forest, and cloud forest) of the Mexican mountains; most of the eastern species (except Yumtaax LCM) are part of the Yumtaax laticornis clade, and the southern and western species are part of the Yumtaax imbellis clade. Species of Yumtaax are distributed in habitats that represent unique genetic reservoirs and that are threated by habitat loss. Resulting data are used to inform management strategies that are required for conservation of the Mexican temperate forests.