Delimiting a constellation: integrative taxonomy of a star-shaped Hydrocotyle species complex (Araliaceae) from the Brazilian Atlantic forest

Species delimitation must overcome the inconsistency among the different delimitation criteria to maintain species as reliable units for biological research and conservation. The general lineage species (GLS) concept embraces different methods of species delimitation and thus provides an integrative framework for taxonomy. The Hydrocotyle stella complex contains six morphotypes that occur along mountain ranges within the Brazilian Atlantic forest, possibly representing undescribed species. In this study, we adopted the GLS concept to assess whether H. stella would be a single species or not, in which we considered genetic structure and morphological discontinuity as evidences for species delimitation. We applied ISSR-based population genetics and morphometrics to 12 populations of H. stella, representing all morphotypes across their main geographical range. Population genetics revealed three genetically structured groups (ΦST > 0.22), each associated with different mountain range regions. Morphometrics indicated significant (p < 0.001) morphological divergence among genetically structured groups, but not for all of the traditional leaf morphotypes. Based on congruency between genetic structure and morphological discontinuity, we recognized three species within the complex, H. alpina, H. palacea, and H. quinqueradiata, and provided their due taxonomic treatment.