Assessing the molecular diversity of Hildaea (Poaceae, Panicoideae): reaching a compromise between the splitter and the lumper

The taxonomy of some groups of plants is challenging, and the strict use of morphological characters may not be enough to solve problems of species delimitation. Hildaea, a genus of tropical grasses recently segregated from Ichnanthus section Foveolatus, is mostly composed of species with obscure boundaries. This group was revised by two authors, Rogers and Stieber, with distinct opinions. The former recognized > 30 taxa, whereas the latter reduced this number to six. In the present study, we re-evaluate current and previous classifications through a comprehensively sampled phylogenetic analysis using plastid (ndhF) and nuclear data (ETS and ITS). Our results demonstrate that the diversity in Hildaea is a middle ground between the splitter and the lumper, indicating that several taxa currently treated as synonyms should be reinstated. Old World Hildaea were found to belong to two clades, one including species from Asia and Oceania, and another including species from the Neotropics and from western Africa. Topological incongruences suggest that hybridization may be a possible cause for the morphological variation observed and also an important evolutionary driver.