Taxonomy and phylogenetic insights for Mexican and Central American species of Acer (Sapindaceae)1

The understanding of the species traits of Acer L. growing in subtropical and tropical America is relevant because this region represents its most southern geographic range in the hemisphere. This study evaluates the morphological variation and updates the taxonomic status, distribution, and phylogenetic relationships of Acer in Middle America. A total of eight taxa are recognized. The presence of Acer negundo subsp. mexicanum is documented for Honduras, while five taxa are restricted to northern Mexico (Acer negundo var. arizonicum, A. negundo var. texanum, Acer glabrum var. neomexicanum, Acer grandidentatum, Acer grandidentatum var. sinuosum), whereas Acer binzayedii is endemic to western Mexico. Only Acer skutchii and A. negundo subsp. mexicanum are widely distributed in the investigated area. The populations are often fragmented and disjunct. The phylogenetic analysis identifies the A. grandidentatum populations from northwestern Mexico as a separate lineage. Descriptions, distribution maps, photographs, and conservation assessments of the species as well as a key to species are provided.