Phylogenetics of the Andean tree genus Ruagea (Meliaceae): implications for taxonomy

Ruagea (Meliaceae) comprises c. 15 species of small or medium-sized trees distributed in Central and South America, predominantly in montane rain forest and cloud forest of the Andes. The taxonomic position of Ruagea has changed several times in the past, and it was previously included in Guarea. Ruagea is currently accepted as a separate genus based on morphology and molecular phylogenetic analyses at the family level. However, its monophyly has not been accurately tested, and phylogenetic relationships among species are still largely unknown. In addition, delimitation of species boundaries is not straightforward due to morphological diversity within species. Here, we present the first phylogenetic reconstruction of Ruagea based on two nuclear ribosomal (ITS, ETS) and two plastid DNA regions (rps4-trnT, psbA-trnH). Our results show that Ruagea is monophyletic and composed of four main clades (A, B, C and D). Clade D, comprising the Ecuadorian endemic R. membranacea and a potentially new species from Colombia, is sister to the rest of the genus. Our results demonstrate that R. membranacea and R. insignis are monophyletic and provide support for the recognition of two new species with divergent morphologies. The delimitation of the remaining species remains unresolved as they are recovered as either poly- or paraphyletic. Our results highlight the complexity of the taxonomy of Ruagea, as found in other rainforest taxa, and the need for further detailed analyses to delimit these taxa. This study provides the first and most extensive phylogenetic analysis of the genus so far, representing a contribution towards understanding the evolutionary history of Ruagea.