Phylogenetic Relationships of the Monotypic Genus Amphianthus (Plantaginaceae Tribe Gratioleae) Inferred from Chloroplast DNA Sequences

Within the past decade, Scrophulariaceae sensu lato has been shown to be polyphyletic and, as a result, is currently undergoing major systematic revision. The traditionally recognized family is now generally considered to comprise several smaller families including the newly expanded Plantaginaceae, a family of 12 tribes, 92 genera, and approximately 2000 species. Recent evidence from molecular phylogenetics supports the inclusion of the tribe Gratioleae within the Plantaginaceae. Gratioleae includes 16–40 genera, depending on generic circumscription, many of which have yet to be assessed phylogenetically. Amphianthus is a monotypic genus whose systematic affinities have long been poorly known. We included Amphianthus, 10 additional Gratioleae genera, and several outgroup genera from Plantaginaceae in a phylogenetic investigation to examine the relationships of Amphianthus. We present the most complete phylogeny of the Gratioleae to date and provide evidence from chloroplast DNA sequences of the ndhF gene and the trnS–trnG–trnG intergenic spacer and intron that unequivocally place Amphianthus within Gratiola, and discuss the morphological evidence supporting our findings. Based on this evidence, we transfer the sole species of Amphianthus (Amphianthus pusillus) to Gratiola, establishing the new name Gratiola amphiantha and placing Amphianthus in synonymy with Gratiola.