Phylogenetic analysis of the Santolina rosmarinifolia aggregate (Asteraceae: Anthemideae: Santolininae) based on morphological characteristics

The phylogenetic relationships between taxa of the Santolina rosmarinifolia aggregate were studied using TNT and PAUP parsimony analyses of a morphological data matrix that encompasses 2516 individuals. Two major clades can be distinguished: clade 1 comprises S. semidentata, S. melidensis, S. impressa, S. orocarpetana and S. xoblongifolia; clade 2 comprises S. ageratifolia, S. canescens and the subspecies arrabidensis, rosmarinifolia, castellana, pectinata and montiberica. No qualitative characteristics or groups of characteristics clearly differentiate these clades. Monophyly of the S. rosmarinifolia aggregate is supported. Most populations appear highly polyphyletic. Santolina impressa, S. melidensis, S. ageratifolia and the S. rosmarinifolia subspecies rosmarinifolia and arrabidensis form a monophyletic group whereas Santolina orocarpetana is polyphyletic and Santolina oblongifolia, S. canescens, S. semidentata and the subspecies castellana, pectinata and montiberica are all paraphyletic. The internal branches have an average length of 20.1 steps, with a standard deviation of 8.5 steps. The basal branch of several taxa shows a much higher number than average (20.1 steps) over the tree, which suggests that reasonably good clade support is present for these taxa. Santolina semidentata is the most variable taxon of this aggregate. The presence of a capitulum with three rows of involucral bracts is the ancestral condition in the aggregate. The results suggest that this aggregate arose from an ancient polyploid. A key to the taxa is provided.