Genus: Cell body long cylindroid, with a slight constriction at the center, where a folded structure present; both ends truncated, smooth; chloroplasts consist of a central rod and irregularly arranged laminae; about 6-8 pyrenoids (Illustrations of The Japanese Fresh-water Algae, 1977). Species: Cell body elongated, 165- (176-246) -300 μm long, 9.5- (12.6) -20 μm wide, L/W=12-18; semicells slightly tapered at blunt end, laterally wavy (7-8 waves); 6-7 folds at base; cell wall dotted (Illustrations of The Japanese Fresh-water Algae, 1977).

31 μm 63 μm 94 μm; x 640

Docidium undulatum Bailley, cell body about 175 μm long, 14 μm wide, L/W=, x 640, Mida-ga-hara (bog/marsh), Gassan (mountain), Tsuruoka city (formerly Haguro town) & Shonai town (formerly Tachikawa town), Yamagata Pref., Japan, August 3, 2006 by Y. Tsukii

Docidium undulatum Bailley, cell body 174 μm long, 14 μm wide, L/W=, x 640, Mida-ga-hara (bog/marsh), Gassan (mountain), Tsuruoka city (formerly Haguro town) & Shonai town (formerly Tachikawa town), Yamagata Pref., Japan, August 3, 2006 by Y. Tsukii

Images of collecting locality: No. 3, Mida-ga-hara (bog/marsh), Gassan (mountain), Tsuruoka city (formerly Haguro town) & Shonai town (formerly Tachikawa town), Yamagata Pref., Japan, August 3, 2006 by Y. Tsukii