The Conundrum of Shrub Oaks in Mexico

Oscar De Luna Bonilla, Susana Valencia-A., and Antonio González Rodríguez

Published May 2026 in International Oaks No. 37: 265–274

Abstract

Shrub oaks constitute a distinctive yet understudied component of the genus Quercus. In Mexico, several taxa of shrub oaks display complex patterns of morphological similarity and overlapping distributions. In this study, we focused on a species complex related to Q. microphylla, integrating morphological, ecological, and molecular evidence to reassess species boundaries and uncover hidden diversity. We analyzed 35 populations representing 6 problematic taxa across 3 major biogeographic provinces in Mexico. Leaf shape variation was quantified through geometric morphometrics, complemented by trichome characterization and ecological niche modeling. Nuclear microsatellite markers were used for some of the taxa to evaluate genetic structure, and an integrative assignment framework was implemented to synthesize the different evidence sources. Our results revealed the presence of 2 major morphological and geographic groups within the complex, as well as atypical populations previously assigned to Q. frutex and Q. striatula. Subsequent focused analyses supported the recognition of 2 new species, Q. oyamae (unpublished) and Q. purhepecha Luna-Bonilla, Valencia & Coombes, both characterized by restricted distributions and distinctive morphological traits. More broadly, this work provides a first step toward refining the taxonomic framework of the Q. microphylla complex and contributes to a better understanding of the evolutionary and ecological dimensions of shrub oak diversity.

Keywords

Quercus microphylla, integrative taxonomy, newly described species, species complex

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