Phylogenetic relationships in tribe Buddlejeae (Scrophulariaceae) based on multiple nuclear and plastid markers

Abstract

Buddlejeae comprise c. 108 species in five commonly accepted genera: Buddleja, Chilianthus, Emorya, Gomphostigma and Nicodemia. Conflicting generic and infrageneric level classifications based on morphology attest to a need to evaluate relationships and trait evolution in a molecular phylogenetic framework. We use multiple independent loci from the nuclear and plastid genomes and representative taxonomic sampling to infer phylogenetic relationships using maximum likelihood and Bayesian analyses with single-locus and concatenated data and Bayesian multispecies coalescent analyses. Nicodemia and Gomphostigma are resolved as monophyletic. Chilianthus is not monophyletic, with three species in one clade and Buddleja glomerata (=Chilianthus lobulatus) possibly separate. Buddleja is paraphyletic with respect to Chilianthus, Emorya, Nicodemia and, probably, Gomphostigma. We propose a new classification to reflect phylogenetic relationships in Buddlejeae. Only Buddleja is retained at the generic level. Chilianthus, Nicodemia, Gomphostigma and Emorya are combined with Buddleja, with a new name and new combination erected for the two Emorya spp., Buddleja normaniae and B. rinconensis. Sectional classification of Buddleja is revised, with two new monotypic sections being proposed, Salviifoliae and Pulchellae, and Gomphostigma being lowered to sectional rank. Reproductive morphological traits traditionally used to define genera, including stamen exsertion, corolla shape and inflorescence type, were reconstructed on the phylogenetic tree and are inferred to have converged on similar states multiple times. Plesiomorphic trait states in Buddlejeae include capsular fruits, included stamens, white and tube-shaped corollas and paniculate inflorescences.