Four new species of Mapania Aubl. from montane habitats in Guyana are described. A new combination at new rank, Scleria subeggersiana (Kük.) Camelb. & Goetgh., is published for Scleria microcarpa Nees ex Kunth var. subeggersiana Kük. The new combination Cephalocarpus spongiosus (M. T. Strong) M. T. Strong and the replacement name Rhynchospora hollowellii M. T. Strong, replacing the later homonym R. capillifolia W. W. Thomas, are published. Typifications are made for 30 names representing 27 currently accepted names in Cyperaceae occurring in the Guianas, South America: Becquerelia glomerulata Brongn. [var. euglomerulata] f. rubra H. Pfeiff., Calyptrocarya intermedia C. B. Clarke, Cephaloschoenus globosus (Kunth) Nees var. minor Nees, Cyperus cornelii-ostenii Kük., Cyperus jenmanii C. B. Clarke ex Morong, Cyperus oxylepis Nees ex Steud., Cyperus radiatus Vahl var. elongatus Boeckeler, Cyperus traillii C. B. Clarke, Dichromena pubera Vahl, Eleocharis filiculmis Kunth, E. homonyma Steud., E. jelskiana Boeckeler, E. nana Kunth, E. septata Miq., E. subfoliata C. B. Clarke, Haloschoenus emaciatus Nees, Mariscus chlorocephalus C. B. Clarke, Pleurostachys orbignyana Brongn., R. curvula Griseb., R. heterocaulis C. B. Clarke, Schoenus asper Schrad., Schoenus setaceus P. J. Bergius, Scirpus maculosus Vahl, Scleria bracteata Cav., Scleria grandifolia Miq., Scleria kunthii Miq., Scleria liebmannii Steud., Scleria reflexa Kunth var. surinamensis Boeckeler, Scleria stipularis Nees, and Scleria tuberculata Boeckeler. The identity of the holotype of Scleria microcarpa Nees ex Kunth var. longiligula Nees is clarified.