Hidden in plain sight: a new species of Pleurothallis (Orchidaceae: Pleurothallidinae) from Colombia previously misidentified as Pleurothallis luctuosa

Pleurothallis tenuisepala, a new species in subsection Acroniae, is described and compared to Pleurothallis luctuosa with which it has previously been confused. While the two species are superficially similar, they can be very easily distinguished by the size of the flowers, which are approximately 60 mm long in P. tenuisepala versus approximately 29 mm long in P. luctuosa, or the length of the sepals, which are approximately four-times the length of the petals in P. tenuisepala versus less than twice the length of the petals in P. luctuosa. The two species can also be discriminated by their nuclear internal transcribed spacer (nrITS) sequences. Pleurothallis tenuisepala occurs on Isla Gorgona off the Pacific coast of Colombia and on the western slopes of the Cordillera Occidental of the Colombian Andes, while P. luctuosa is restricted to the Cordillera de Tilarán of Costa Rica. Labellar micromorphology of both species is discussed in relation to possible pollination mechanisms. Key words: Acroniae, cryptic species, labellum, morphology, taxonomy