Isoëtes Cleefii, known so far from four localities in the Colombian Páramo of the Cordillera Oriental between 3745 m s.m. and 4245 m s.m., is described as a further new taxon of the section Laeves. It is dedicated to the Dutch botanist and collector Antoine Marie Cleef (1941 – x ) who added substantially to the knowledge of ecology and distribution of the Colombian Quill-worts thanks to his rich collections gathered between 1971 and 1973.