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.

Evolution of anatomical characters in Acianthera section Pleurobotryae (Orchidaceae: Pleurothallidinae)

“…The analysis of molecular data combined with anatomical and micromorphological data of Acianthera section Pleurobotryae allowed us to identify shared anatomical characters observed exclusively in these species, besides supporting the internal relationships suggested by the molecular data set [ 15 ]: unifacial leaves, round or elliptical in cross-section, round leaves with vascular bundles organized in concentric circles, and mesophyll with 28 to 30 cell layers. Cladistic analyses also revealed shared homoplastic characters, such as the presence of three sclerified cortical cell layers in the ramicaul, absence of tracheoidal idioblasts in the mesophyll and labellum with round apex.…”

“…A total of 15 species of Acianthera was studied, covering eight of the nine sections of this genus ( Table 1 ). The species Pleurothallopsis nemorosa Porto & Brade was included as outgroup, based on recent phylogenetic studies of the section [ 15 ].…”

“…All characters were equally weighted and with unordered states [ 50 ]. Molecular data for nuclear (nrITS) and plastidial (cpDNA matK) DNA were obtained from Rodrigues et al [ 15 ] ( Table 1 ).…”

“…Phylogenetic relationships were also evaluated through Bayesian inference using Mr Bayes 3.1 [ 53 ]. Evolution models used for molecular data follow Rodrigues et al [ 15 ]: K80+G for ITS1, K80 for 5.8S and HKY+G ITS2 (nrITS) and GTR+G for matK. The model used for the morphological data partition was mk1 [ 54 ].…”

“…Recent phylogenetic analyses, based on nuclear ITS and chloroplast matK sequences, recovered A . section Pleurobotryae as a strongly supported monophyletic group and the group diagnosis requires the occurrence of cylindrical or laterally compressed leaves along with a filiform caulome [ 15 ].…”