Phylogeny of Aconitum subgenus Aconitum (Ranunculaceae) inferred from ITS sequences

Abstract

Nuclear ITS sequence data were used to investigate phylogenetic relationships within Aconitum subgenus Aconitum, which is well-known for its taxonomic complexity. We selected 51 species and one variety of this subgenus from eastern Asia, North America and Europe, mostly from the Hengduan Mountains region in southwestern China and representing all the previously circumscribed infrasubgeneric groupings. Traditional circumscription of some infrasubgeneric taxa is not supported by our data, and the relationships of the species in these taxa should be reconsidered. Species from northern China show relatively close relationships with those from Europe, North America, Japan and Korea of eastern Asia. High morphological variation but low genetic diversity found in species from the Hengduan Mountains region probably indicates a recent radiation. Our ITS topology is congruent well with the subgrouping of the subgenus Aconitum based on the morphology of seeds and of petals, suggesting that seed and petal morphology may reflect well the phylogenetic relationships within the subgenus, but other morphological characters which have long been previously considered to be of important systematic value, i.e. the degree of leaf division, the shape of the upper sepal and the attitude of the stem, might be unreliable in subdividing the subgenus.