A new species belonging to Rubiaceae, Psychotria niauensis Butaud & J.Florence, sp. nov., is described from the uplifted atoll of Niau in the Tuamotu archipelago in French Polynesia. Morphologically isolated in French Polynesia, this new species is close to P. leiophylla Merr. & L.M. Perry from Melanesia and Western Polynesia, a species linked with several Psychotria L. recently transferred in Eumachia DC. Study of the characteristic criteria of both genera confirmed the placement of both species in Psychotria due to their pink, purple or violet fruits, an apical pore in the smooth pyrene and a seed coat with ethanol-soluble pigment. Psychotria niauensis sp. nov. can be distinguished from P. leiophylla by its always pedunculate inflorescences, with a longer peduncle of more than 3.5 cm long, by ovoids pyrenes (vs subellipsoid to subgloboid) and smaller less than 3 mm wide, and by smaller petioles less than 1 cm. It can be distinguished from all Eastern Polynesian species of Psychotria by inflorescences counting more than 50 flowers, by flowers less than 7 mm diameter, by violet fruits at maturity, by the smooth dorsal side of the pyrene, and by its particular ecology, growing on calcareous soil. Sole representative of the genus in the Tuamotu archipelago, known by less than 80 individuals and threatened, among others, by urbanization close to the main population, this species is considered as “endangered” [EN] according to IUCN criteria. In order to preserve this rare species, we recommend to add it to the list of protected species of the environmental regulations of French Polynesia, but also to give a conservation status to the natural forests which harbor it together with other endemic or protected species like Myrsine niauensis Fosberg & Sachet, Glochidion tuamotuense J.Florence or Pritchardia mitiaroana J.Dransf. & Y.Ehrhart.
Psychotria, Pacific, French Polynesia, Tuamotu, atoll, calcareous, conservation, botanical survey, new species