An overview of the phylogenetic relationships within Epidendroideae inferred from multiple DNA regions and recircumscription of Epidendreae and Arethuseae (Orchidaceae).

Phylogenetic relationships within the epidendroid orchids with emphasis on tribes Epidendreae and Arethuseae were assessed with parsimony and model-based analyses of individual and combined DNA sequence data from ITS nuclear ribosomal DNA and plastid trnL intron, the trnL-F spacer, matK (gene and spacers), and rbcL regions. Despite the absence of boostrap support for some of the relationships, a well-resolved and supported consensus was found, for which most clades were present in more than one individual analysis. Most clades of this consensus attained high posterior probabilities with a Bayesian approach. Circumscription of Arethuseae and Epidendreae are different from most orchid systems based on morphology, but they correspond to a combination of patterns from several less comprehensive orchid phylogenetic analyses previously published. A new circumscription of Epidendreae includes only Neotropical subtribes (Bletiinae, Chysiinae, Laeliinae, Ponerinae, and Pleurothallidinae), whereas Arethuseae include Coelogyninae (all Old World) and Arethusinae (pantropical). Many previously included genera will need to be moved to other tribes. Taxa previously assigned to be Old World Epidendreae are related to different groups of Old World orchids, and this study can serve as a guide for sampling strategies in future studies to resolve troublesome epidendroid orchid clades.