New infrageneric classification of Abies in light of molecular phylogeny and high diversity in western North America

Abies Mill. represents one of the most diverse lineages in Pinaceae with ca. 50 species. Recent phylogenetic studies of Abies using regions of the nuclear and plastid genomes generally support recent classifications. However, we have previously shown that in several cases sectional memberships should be revised, and more species are needed to generate a robust infrageneric classification. Therefore, we present a revision of Abies taxonomy based on phylogeny using the most comprehensive taxon sampling (52 taxa worldwide) to date and five chloroplast gene regions and one single-copy nuclear gene (LFY). Our phylogenetic analyses, including maximum parsimony, maximum likelihood, and Bayesian inference, yield seven well-supported lineages that are consistent with previous studies. Our taxonomic revision integrates the phylogenies presented here as well as those from other studies. We merged sect. Pseudopicea with sect. Momi, recognized the merger of sect. Abies with sect. Piceaster, and sect. Grandis with sect. Oiamel. We recognized sect. Balsamea by excluding A. kawakamii (Hayata) T. Ito and we suspect that ancient hybridization was involved in its origin. A short morphological description is provided for each section, as well as its geographic distribution and list of accepted names of species. Five of the seven sections consist primarily of species in western North America, especially within the California Floristic Province. Phylogenetic results show that western North America is home to an exceptionally high diversity of fir lineages, which is further corroborated by the cuticle morphology and internal transcribed spacer genotypes based on the length differences.