The family Cyperaceae is cosmopolitan and includes some 115 genera and 3 600 species. Costa Rica has 25 genera and 210 species. Here I present keys and descriptions for 34 species (10 genera) that occur in La Selva Biological Station, Costa Rica. The genus Cyperus is represented by 12 species, followed by Rhynchospora (6), Scleria (5), Calyptocarya (2), Eleocharis (2), Kyllinga (2), Mapania (2), Hypolytrum (1) and Lipocarpha (1). Oxycaryum cubense (Poepp & Kunth) Palla, has been collected in the vicinity and could eventually be found at the Station.
Keywords: angiosperms, cyperaceae, Cyperus, rhynchospora, Scleria, La Selva, Costa Rica.