Molecular Phylogeny of Atractantha, and the Phylogenetic Position and Circumscription of Athroostachys (Poaceae: Bambusoideae: Bambuseae: Arthrostylidiinae)

Atractantha and Athroostachys are Neotropical woody bamboo genera (Poaceae: Bambusoideae: Arthrostylidiinae) that occur mainly in the Brazilian Atlantic forest from Bahia to Rio de Janeiro, with a single Atractantha species in southern Venezuela and in northwestern Amazonas state in Brazil. Previous phylogenetic studies resolved Atractantha as monophyletic, however, only three of its six species have been sampled. The aims of this study were to test the monophyly of Atractantha based on a broader sampling of the genus, and to investigate the phylogenetic position of the monotypic Athroostachys, previously unsampled in any molecular phylogeny. Seven plastid regions (ndhF, rps16, rpl16, trnC-rpoB, trnD-trnT, rps16-trnQ, and trnT-trnL), both coding and non-coding, were analyzed for 38 species of Arthrostylidiinae and eight species of other subtribes of Bambuseae. Bayesian inference and maximum likelihood analyses were performed for individual regions and the combined plastid dataset. Atractantha, in its current circumscription, is polyphyletic. Atractantha shepherdiana is strongly supported as sister to Athroostachys capitata, and this lade is strongly supported as sister to Merostachys. Besides the molecular evidence, morphological data support the transfer of A. shepherdiana to Athroostachys. The new combination Athroostachys shepherdiana and a new description of Athroostachys are here proposed. A key to the two species of Athroostachys herein recognized and an illustration of the main distinguishing vegetative features of both species are provided.