Cypella (Iridaceae): What do we know about the diversity of the genus? Cypella is a genus centered on the grasslands in Southeast South America, which can be recognized by its flowers with inner tepals having a dense area of glandular trichomes located in a central depression, style branches well developed, compressed, divided above in three crests, two of them acute and positioned in the adaxial part, and the other crest is abaxial and displays a transverse stigmatic surface. A key to distinguish Cypella and related genera is supplied. In this study are recognized 31 species and five subspecies of Cypella: C. Alonsoana, C. amambaica, C. aquatilis, C. armosa, C. aurinegra, C. catharinensis, C. charruana, C. crenata, C. curuzupensis, C. discolor, C. exilis, C. fucata, C. gloriana, C. guttata, C. Hauthalii, C. Herbertii (subspecies Herbertii, brevicristata, reflexa and Wolffhuegelii), C. laeta, C. lapidosa, C. laxa, C. luteogibbosa, C. magnicristata, C. opalina (subspecies opalina and minuticristata), C. Osteniana, C. Pabstiana, C. parviflora, C. pusilla, C. Ravenniana, C. rivularis, C. suffusa, C. trimontina, and C. uliginosa. Comments about geographic distribution, taxonomic affinities, and morphology of all taxa are presented, and a key to distinguish the species of Cypella was organized. Several taxonomic novelties are treated, C. opalina is a new status and combination proposed, C. opalina subsp. minuticristata is a new combination recommended, lectotypes are designated for C. curuzupensis, C. lapidosa and C. opalina. New lectotypes are selected for C. Herbertii and C. laeta, explaining the reason for the rejection of the previously chosen lectotypes for these two species. Furthermore, C. boliviana, C. brasiliensis, C. geniculata, C. oreophila and C. unguiculata are excluded of the genus, and the generic placement of them is commented, while C. craterantha, C. elegans and C. Herbertii subsp. reflexa f. palmeti are considered doubtful taxa.