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We determined the phylogenetic relationships, population history, and hierarchical structure of genetic variation in pocket gophers distributed on the Baja California Peninsula (BCP), based on extensive geographic sampling. Using a fragment of the mitochondrial gene cytochrome b (cyt b), we found three latitudinal structured geographic clades (northern, central, and southern). The northern clade occurs in the border area of the USA and the north of BCP, the central clade occurs from the peninsular highlands through the Central Desert of Baja California, and the southern clade is distributed south of the San Ignacio Lagoon. AMOVA showed that genetic variation is higher among clades (64%) than within populations (18.1%). The deepest divergence among clades is very shallow (similar to 300 000 years), which suggests that climatic changes during the Pleistocene or some inhospitable habitats have affected the structure of this group, rather than influences from older marine transgressions. Phylogenetic groups disclosed by our results do not coincide with the current infraspecific classification; therefore, we propose a change of epithet for BCP gophers (Thomomys nigricans) and a new subspecific taxonomic arrangement with four subspecies: Thomomys nigricans anitae, Thomomys nigricans martirensis, Thomomys nigricans nigricans, and Thomomys nigricans russeolus. (C) 2013 The Linnean Society of London