The taxonomic status of the Mexican oak Quercus undata (Fagaceae, Quercus, Section Quercus)

Abstract

Quercus undata Trel. (Fagaceae, Quercus, Section Quercus) has a complex taxonomic and nomenclatural
history. Intensive sampling of oaks at the type locality of Q. undata Trel. in Durango, Mexico and evaluation of
herbarium specimens and plants in the field indicate that Q. undata represents variation in Quercus chihuahuensis Trel.
in white oak communities where introgressive hybridization among Q. chihuahuensis, Q. grisea Liebm., and a third
white oak, Q. arizonica Sarg. made species identification difficult. Endlich’s type specimen of Q. undata, as designated
by Trelease, was apparently destroyed in bombing raids on Berlin during World War II, and we propose herein as
lectotype the Trelease illustration of the type. An epitype is also designated in support of the lectotype, given that some
features cannot be critically observed on the illustration. The long peduncles of the specimen illustrated by Trelease
indicate a close relation to Q. chihuahuensis.