In this study we use a combination of morphological, molecular (mtDNA cytochrome c oxidase subunit 1 gene), geographic and ecological (field observations and cpDNA sequences from ingested plant tissue) data to describe and diagnose a new southern Nearctic leaf beetle species of Calligrapha Chevrolat, 1836 (Chrysomelidae: Chrysomelinae): Calligrapha thermalis Gómez-Zurita, sp. nov., associated to Perymenium mendezii De Candolle (Asteraceae). This new species, restricted to the Sierra Madre Occidental, is closely related to the Texan endemic Calligrapha wickhami Bowditch, 1911 associated to Viguiera stenoloba Blake (Asteraceae) in the northern foothills of the Sierra Madre Oriental ecoregion. The evolutionary scenarios explaining this recent taxonomic split, dated in the Pleistocene, are laid out and discussed.