Phylogeny, Phenotypic Evolution, and Biogeography of the Scutellaria angustifolia Complex (Lamiaceae): Inference from Morphological and Molecular Data

Abstract

Independent analyses of phylogenetic relationships in the Scutellaria angustifolia complex were carried out using both molecular and morphological data. A best estimate of the phylogenetic relationships among the 10 taxa of the S. angustifolia complex is derived from a synthesis of the molecular and morphological analyses. This approach provides greater resolution than the congruence approach and retains the interpretative value of using two independent data sets, which would be lost if the data were combined. The phylogency based on morphology is both less well resolved than, and not congruent with, the phylogeny based on molecular data. However, morphology provides important clues to help resolve one portion of the phylogeny that is poorly resolved using the molecular data. The best estimate of phylogeny for the group is then used to interpret the evolution of vegetative and reproductive characters, habitat preference, and biogeography. The results suggest that long-flowered, outcrossing species have evolved in parallel on three separate occasions from short-flowered, more highly selfing species, a trend that is atypical in flowering plants. Three taxa are identified as having morphologies that are apprently ancestral to other taxa, thereby furnishing an example of morphological stasis without evidence from the fossil record. The evolution of habit preference generally has been from wet to dry sites and the biogeographic history of the group is one of eastward dispersal accompanied by speciation from an origin in California [USA].