Scenedesmus, genus of about 70 species of colonial green algae (family Scenedesmaceae), a common component of freshwater plankton. Scenedesmus species are used experimentally to study pollution and photosynthesis and are a potential source of biodiesel. In sewage purification processes, the algae provide oxygen for the bacterial breakdown of organic matter and thereby help to destroy other harmful substances.
Scenedesmus species are nonmotile and usually consist of 4, 8, 16, or 32 cells arranged in a row. Some species are spiny or feature bristles. Reproduction is by nonmotile spores called autospores.