A fl oristic and ultrastructural study on naked green Euglenophyta was performed in the Amazonian and Caribbean regions of Colombia, where a large number of taxa are contained in several freshwater bodies. A total of 37 taxa were recorded, 1 belonging to the genus Cryptoglena Ehr., 9 to Lepocinclis Perty, 1 to Monomorphina Meresch., and 26 to Phacus Duj. From the identifi ed taxa, 22 were recorded for the fi rst time in Colombia, 2 in the Amazonian region, and 14 in the Caribbean region. Among the taxa described in this work we propose Phacus sesquitortus var. longicauda as a new variety. In addition, 9 taxa were examined by scanning electron microscopy (SEM) to illustrate in detail their ultrastructure; 3 of them were examined for the fi rst time under this method.