Pachygenium laurense (Orchidaceae, Spiranthinae), a new orchid species from Argentina-morphological evidence and phylogenetic reconstruction

Background. Pachygenium embraces a group of terrestrial species formerly placed in Pelexia sensu lato. The genus currently comprises some 60 species, most of which are known from the southern parts of Brazil and Paraguay, with few species distributed in the Andean countries???only four species have been recorded from Argentina so far. In Jujuy Province, Argentina a new species of Pachygenium was found during our fieldwork. The aim of this article was to provide morphological and molecular evidence for its membership in this genus. Methods. Materials from specimens were collected in the field and examined by classical taxonomic and molecular biological techniques, e.g., PCR and sequencing DNA. Phylogenetic reconstruction was performed by maximum-likelihood and Bayesian inference. Results. Pachygenium laurense from Argentina is described and illustrated based on morphological evidence and its taxonomic position was confirmed by phylogenetic analyses. A new combination for Pachygenium gutturosa is also proposed. A key for identification is provided for the Pachygenium species occurring in Argentina. Conclusion. Pachygenium laurense is the fifth species of the genus recorded from Argentina.