Species [ var. trabecula ]: Vegetative cells cylindrical, 260-660 μm long, 24-45 μm diam., L/W=11-18, constricted at center, semicells bulged at base; chloroplast elongate, with 3-4 laminae; cell wall dotted. [ var. rectum (Delponte) W. et G.S. West ]: Cell body thinner than var. trabecula, 180-493 μm long, 14-23 μm wide, L/W=12-18. [ var. crassum Wittrock ]: Cell body shorter and wider than var. trabecula, 275-554 μm long, 30-57 μm wide, L/W=6-7 (not exceed 10). [ var. elongatum Cedergren ]: Cell body longer than var. trabecula, 600-830 μm long, 30-40 μm wide, L/W=19-28. [ var. maximum (Reinsch) Roll ]: Cell body 350-1120 μm long, 44-65 μm wide, L/W=8-17 (Illustrations of The Japanese Fresh-water Algae, 1977).

50 μm 100 μm 150 μm; x 400 : 31 μm 63 μm 94 μm; x 640