A new species of (Hymenoptera, Formicidae) fungus-growing ant from the Sierra Madre Oriental of northeastern Mexico.

Here we describe a new species of , , from the Gran Sierra Plegada range of the Sierra Madre Oriental, in the states of Coahuila and Nuevo Leon, northeastern Mexico. is a large-sized species compared to other North American . Its geographic distribution includes the piedmont of the Gran Sierra Plegada at La Estanzuela, Monterrey, as well as peripheral mountains segregated from the Sierra Madre Oriental (Cerro de las Mitras, Sierra de Zapalinamé, Cañon de San Lorenzo, Cerro de las Letras). The preferred habitats of include oak-pine forest at La Estanzuela, xeric oak forest at Zapalinamé and mesic Chihuahuan desert scrub with sotol () at other sites. All localities are on slopes, on very rocky, shallow lithosols overlaying large boulders. This species nests under and between large boulders and rocks. It has not been observed on alluvial or better developed, deeper soils, and it is absent from sites with human activity (urban, disturbed, and landscaped areas). It is closely related to and morphologically similar to . The known distribution ranges of and almost overlap in Saltillo, Coahuila state. The main character that distinguishes the new species from is longer antennal scapes in ; also, different nesting habits (rocky slopes vs. alluvial sites or deep sand in ), and geographic distribution. Phylogenetic analysis of DNA sequences from the mitochondrial marker () and the first intron of the F1 copy of the nuclear protein-coding gene Elongation Factor 1- α -α- confirm a sister-species relationship between and . Bayesian coalescent analyses indicate a divergence time of about 8.00 million years before present (95% confidence interval: 4.8-11.5 mya) between and . The divergence of the lineages of and could have been driven by the Pliocene-Holocene desertification of southwestern North America. This process resulted in isolated mesic refugia and forests in the Madrean ranges and piedmonts of northeastern Mexico (the current habitat of ) while adapted to the deeper, often sandy soils on the drier desert plains of Coahuila and Chihuahua states in Mexico, and New Mexico and Texas in the USA. Within the Nearctic species of the species group, is the species that is closest (by geographical distribution) to Neotropical species of like .