A New Species of Brachystele (Spiranthinae, Orchidaceae) with Nonresupinate Flowers from Central East Argentina

Brachystele morronei, a new orchid species recently discovered in the central-eastern region of Argentina, is described and illustrated. It is the first known species with nonresupinate flowers of the Pelexia clade, constituting a very distinctive member of the group. The phylogenetic position of the new taxon was inferred from nuclear ribosomal DNA (ITS) and two plastid DNA regions (matK and trnLF). The combined nuclear and plastid data analyses using Bayesian and parsimony-based methods revealed that B. morronei is closely related to B. camporum. The geographic distribution and a conservation assessment of the new species are presented. Morphological differences among sympatric Brachystele species are described.