Integrative taxonomy of three Mexican shrub oak species with the description of a new taxon, Quercus oyamae

The shrub oaks of Quercus section Quercus have been poorly studied in Mexico. Within these shrub oaks, Quercus microphylla and morphologically similar taxa (i.e., the Q. microphylla complex) still exhibit a great deal of taxonomic uncertainty related to species identity and delimitation. Quercus striatula is a name in this complex to which morphologically divergent population groups have been associated. Applying an integrative taxonomy approach, we used morphology and geometric morphometrics, genetic analyses with nuclear microsatellite markers, and ecological niche models, to establish the boundaries between morphologically different populations within Q. striatula, in conjunction with Quercus cordifolia, a morphologically close species. Our results support a clear separation of three taxa, which allowed us to propose Quercus oyamae as a new species for science, which corresponds to plants from the Mexican Plateau previously considered as Q. striatula. The new species is described and illustrated and a key for its identification is included.