Genus: Cell body long cylindroid; a slight constriction at center; cross section of the semicells spherical, slightly swell at the center but without a folded structure as Docidium; slightly tapered toward both ends, which are truncated and smooth or surrounded by granules or various small structures; laterally straight or wavy, with spiny projections in some species; 2-10 ribbon-like chloroplasts in each semicell; with many pyrenoids; a vacuole containing active granules at both ends same as in Closterium; cell wall mostly dotted, but with spines or other patterns in some species (Illustrations of The Japanese Fresh-water Algae, 1977).
Species:

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var. nodosum:
P. nodosum v. nodosum 300 x 47 μm Inari Park Toyama, 2002	P. nodosum v. borgei 505 x 68 μm x 200 Uruguay, 1999
var. borgei: Lateral waves larger than var. nodosum
P. nodosum v. borgei ? μm Numappara marsh Kuroiso Tochigi, 2003	P. nodosum v. borgei ? 302 x 52 μm Numappara marsh Kuroiso Tochigi, 2007	P. nodosum v. borgei μm Yamakado marsh Nishi-Azai Shiga, 2008	P. nodosum v. borgei μm Kashibaru m.3 Karatsu Saga, 2008
var. borgei??:
P. nodosum v. borgei 350 x 48 μm Tashirodaira m. Hakkoda mountain Aomori, 2005	P. nodosum v. borgei 346 x 50 μm Tashirodaira m.5 Hakkoda mountain Aomori, 2006	P. nodosum v. borgei μm Miyatoko m.3 Minami-Aizu Fukushima, 2008	P. nodosum v. borgei 330 x 52 μm Oze marsh Katashina Gunma, 2006
P. nodosum v. borgei μm Iroha-numa 4 Zao mountain Yamagata, 2008	P. nodosum v. borgei 250* x 45 μm Kodanuki marsh Fujinomiya Shizuoka, 2006	P. nodosum v. borgei μm Kareki-numa Nikko Tochigi, 2008	P. nodosum v. borgei 315 x 50 μm x 400 USA, 1999

Similar species ->> Pleurotaenium kayei; Triploceras; Docidium undulatum;

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