Two new species of Acianthera (Orchidaceae) from the Brazilian Amazon

Acianthera Scheidw. is a genus of Orchidaceae Juss. composed of approximately 300 species, nearly half of which occur in Brazil. To date, only eight species of the genus have been recorded from the Brazilian Amazon. A recent botanical excursion to Serra do Divisor National Park in the state of Acre, in the extreme western portion of the Brazilian Amazon, resulted in the discovery of two new species of Acianthera: A. amazonica Marcusso sp. nov. and A. nukiniana Marcusso sp. nov. Here, we describe these new species and present photographs, illustrations, taxonomic notes and comments on their morphological relationships, and environmental preferences. In addition we assign the conservation status and provide a geographic distribution map, as well as an identification key for Acianthera species from the Brazilian Amazon.