Phylogeny of Acianthera sect. Pleurobotryae (Orchidaceae: Pleurothallidinae), an endemic group of the Atlantic Forest

Abstract

Among the members of subtribe Pleurothallidinae, Acianthera is one of the largest genera in Brazil with ca. 107 endemic species. A recent study of Acianthera, including a phylogeny based on nrITS and a systematic revision, proposed dividing the genus into nine sections. In this revision, the genus Pleurobotryum was reduced to Acianthera sect. Pleurobotryae. However, the true position of this section and its circumscription are debatable because the authors included only one species of the genus and did not include the type species (Pleurobotryum atropurpureum Barb. Rodr.) in the analysis. The objective of this work was to study the monophyly of the section and phylogenetic relationships among the species of A. sect. Pleurobotryae. The study included all of the species in this group and used the nuclear marker ITS (ITS1, 5.8S gene and ITS2) and an initial portion of the plastid marker matK for individual and combined maximum parsimony, Bayesian and maximum likelihood analyses. The results show that A. sect. Pleurobotryae is monophyletic with high bootstrap, decay index, and posterior probability support. Within the group, the results suggest, with moderate to strong support, the recognition of two sister clades: [(Acianthera hatschbachii (Schltr.) Chiron & van den Berg, Acianthera atropurpurea (Barb. Rodr.) Chiron & van den Berg), (Acianthera mantiquyrana (Barb. Rodr.) V. T. Rodrigues & F. Barros, Acianthera crepiniana (Cogn.) Chiron & van den Berg)]. The lack of resolution using only nrITS, the strong phylogenetic signal from the matK, and the combined analyses suggest that more studies are needed to verify the phylogenetic position and circumscription of some of the other sections in the genus. In addition, it is important that type species and morphological characters are incorporated into the definitions of the clades.