Photosynthetic euglenoids represent a large group of flagellates, which could be found in most freshwater, marine and brackish habitats, but also in extreme environments with low pH or in moist soil. The existence of this group has been known for a relatively long led to the description of wide morphological variability. In my contribution, I briefly summarize the possible causes of this morphological variability (effect of the environment and phenotypic plasticity during ontogenesis) and current knowledge about the taxonomy of these protist organisms, showing the most recent changes and descriptions of new genera.