Integrative taxonomy improves delimitation in Hypericum subspecies

Integrative approaches have been very useful to identify diagnostic morphological characters in species delimitation and to understand how abiotic factors influence the geographical distribution of taxa and whether these factors may be driving to specific changes in phenotypic variation patterns. Here we use a South American Hypericum species to discuss the importance of such collaborations for taxonomy. The current classification recognizes four sympatric subspecies within Hypericum rigidum; however, due to the presence of intermediary diagnostic characters, a significant number of specimens cannot be assigned to any of these subspecies. Therefore, since the described subspecies are difficult to differentiate, in this study, we applied ecological and morphometric approaches to evaluate whether the infraspecific classification may be sustained in terms of environmental and morphological variation. Applied statistical analyses make evident the high morphological variation within H. rigidum subspecies and the absence of diagnostic characters that sustain the current infraspecific classification. Multivariate analyses also indicate that the morphologic variation of H. rigidum subspecies does not represent adaptive matching of phenotypes to the environment and, therefore, cannot be explained by phenotypic plasticity nor by ecotypic variation. We also discuss the non-standardization of the subspecies concept in plants. In conclusion, H. rigidum subspecies overlap geographically, ecologically and morphologically and, therefore, we recommend that these phenotypes should not be regarded as subspecies, but as part of one single highly variable species.