Family: Colonies of fixed number of cells (4, 8, 16, 32, or more) arranged 2- or 3-dimensionally; cells spherical, ellipsoidal, polygonal, etc. in shape; chloroplasts 1 or several, plate-like in shape, with 1 pyrenoid; reproduction only by asexual autospores.
Genus: Colonies of 4 (or 2, 8, 16) cells attached side by side, arranged linearly or zigzag; cell body elliptical or spindle or crescent in shape; terminal cells with spiny projections in many species; cell wall usually smooth, but in some species granulated or dented or ridged (Illustrations of The Japanese Fresh-water Algae, 1977).

S. quadricauda spines straight x 640	S. quadricauda spines curved x 640	S. quadricauda 8 cells x 640	S. quadricauda var. biornatus ? x 640
S. protuberans ? x 640	S. acuminatus x 640	S. acuminatus ? x 640	Scenedesmus sp. x 640
Scenedesmus sp. x 640	S. ecornis x 640	S. ecornis ? x 640	Scenedesmus sp. x 640
S. circumfusus x 640