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). Species:

50 μm 100 μm 150 μm; x 400

Scenedesmus acutus (Meyen) Chodat var. acutus: Colonies of 4 (sometimes, 2 or 8) cells; cell body spindle in shape; "outer" cells curved; cell wall smooth; 12-19 μm long, 3-7 μm diam. (Illustrations of The Japanese Fresh-water Algae, 1977).

* Scenedesmus acutus f. alternans Hortobagyi: Cells arranged in a zigzag pattern; 9-22 μm long, 3.5-7 μm diam. (Illustrations of The Japanese Fresh-water Algae, 1977).

Scenedesmus acutus f. antenniformis Uherkovich: All cells straight not curved; 10-14 μm long, 2.5-4 μm diam. (Illustrations of The Japanese Fresh-water Algae, 1977).

* Scenedesmus acutus f. costulatus (Chodat) Uherkovich (Syn: S. costulatus Chodat): Colonies of 8 (sometimes, 4 or 16) cells; 10-17 μm long, 3-6 μm diam. (Illustrations of The Japanese Fresh-water Algae, 1977).

Scenedesmus acutus f. tetradesmiformis (Woloszynska) Uherkovich: All cells tapered at both ends; 8-25 μm long, 2.5-7 μm diam. (Illustrations of The Japanese Fresh-water Algae, 1977).