Abstract
Summary The subtribe Polystachyinae Schltr. (Orchidaceae, subfamily Epidendroideae) in Madagascar and adjacent archipelagos is revised. It comprises the two genera: Hederorkis Thouars, and Polystachya Hook., the latter with four sections. All of the species are described and their typification, history, identification, pollination, distribution and habitat are discussed. The circumscription and distribution of Polystachya bicolor Rolfe, P. mauritiana Spreng. , P. rosellata Ridl., P. virescens Ridl. and P. waterlotii Guillaumin are re-defined. Conservation assessments and distribution maps are included for all the species. A checklist of the genera, sections and species and a key to their identification are provided. Four new species: Polystachya anjahankeliensis Hermans, Nusb. & Burivalova, P. ericoides Hermans & Callm., P. flammulifera Hermans and P. pertliae Hermans, Sieder & Andriantiana are described for the first time.