During the preparation of a taxonomic revision of Rhynchospora sect. Longirostres, we found several scientific names that needed to be lectotypified or neotypified. In addition, Rhynchospora amazonica subsp. guianensis is being recognized at the level of species and requires a new name, Rhynchospora rionegrensis. This species is described and illustrated and differs from R. amazonica by its lateral and terminal, generally turbinate inflorescences, brown spikelet scales, loose fascicles, and longer stylopodium. Lectotypes are chosen for Calyptrostylis longirostris (the basionym of R. rionegrensis), R. amazonica, and R. macrostachya, and a neotype chosen for R. stenocarpa.