Molecular Phylogeny Estimation of the Bamboo Genus Chusquea (Poaceae: Bambusoideae: Bambuseae) and Description of Two New Subgenera

Chusquea is a diverse genus of American woody bamboos, accounting for almost half of the woody bamboo species in the Neotropics. Previous analyses of molecular data have recovered four major lineages within Chusquea, but morphological synapomorphies have been identified only for subgenus Rettbergia. This study estimates a chloroplast phylogeny of Chusquea with a focus on relationships within the large and intractable Euchusquea clade. Phylogenetic analyses were conducted on 40% of the described species in Chusquea, with data from five chloroplast regions and a preliminary survey of the nuclear internal transcribed spacer complex. Several results from previous studies were corroborated, including the presence of two clades formerly comprising the genus Neurolepis and monophyly of subgenus Rettbergia. The clades formerly in Neurolepis are named as Chusquea subgenus Platonic and Chusquea subgenus Magnifoliae based on molecular support and potential morphological synapomorphies. We recovered two strongly supported and five weakly supported clades within Euchusquea, but relationships among these lineages were not resolved and species composition of the clades conflicts strongly with current taxonomic groupings based on morphology. Low resolution of the chloroplast phylogeny estimation, low variability in nuclear data, character conflict, and geographical distribution of chloroplast lineages all suggest a recent radiation of the Euchusquea clade. Given the present weak molecular support for relationships within Euchusquea and the lack of synapomorphic morphological characters to define clades, we recommend the use of the current morphology-based taxonomy as a practical means of assessing and describing diversity in the Euchusquea clade.