Genus: Cell body cylindroid, both ends rounded; cell wall smooth or granulated or longitudinally lined; constriction or bands present in some species; outer cell wall yellowish or brownish; chloroplast has radially-arranged laminae which attached cell wall in full length; one or several pyrenoids in each semicell, aligned in chloroplasts (Illustrations of The Japanese Fresh-water Algae, 1977).
Species: Cell body cylindrical, medium in size, both ends broadly rounded, (56-65)-80 μm long, 20-31 μm wide, L/W=2-2.5; cell wall thick, densely dotted, transparent or brownish in color (Illustrations of The Japanese Fresh-water Algae, 1977).
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P. rufescens
70 x 26 μm
Omine-numa
Tsukiyono
Gunma, 2003
P. rufescens
70 x 25 μm
Omine-numa
Tsukiyono
Gunma, 2006
P. rufescens
67 x 24 μm
Omine-numa 6
Minakami
Gunma, 2007
P. rufescens
70 x 26 μm
Kareki-numa m.
Nikko
Tochigi, 2008
P. rufescens ?
52 x 24 μm
Tanohara marsh 4
Shiga highland
Nagano, 2007
