Isochilostachya Mytnik & Szlach., gen. nov., a new genus of Polystachyinae Schltr. (Orchidaceae)

Abstract

A new genus of Orchidaceae (Polystachyinae), Isochilostachya, is described. It is morphologically similar to Polystachya Hook. but is distinct by the narrower, grass-like leaves arranged in the upper part of the stem, long and acuminate floral bracts and sepals, and long clavate or capitate hairs densely arranged on the lip. A comprehensive description of the new genus is provided. A list of examined specimens and information about distribution, habitat, and altitude for each species are presented. A position of the members of the new genus in the cladogram recently obtained from molecular analyses of Polystachyinae is briefly discussed. A taxonomic key to Polystachyinae is included. Eleven new combinations on species level are validated. Eight lectotypes are designated. Most of the species of Isochilostachya are endemic to particular mountains of the Eastern Arc (Eastern Afromontane hotspot) in north-east Tanzania therefore a brief discussion about their restricted distribution is provided.