Genus: Colonies of a fixed number of cells, flat, circular in shape; cell body polygonal in shape, with horn-like projections; cell wall garanulated, wrinkled or notched; chloroplasts plate-like or reticular; asexual reproduction by zoospore; sexual reproduction by isogametes (Illustrations of The Japanese Fresh-water Algae, 1977).
Species: Young colonies with large perforations between the cells; marginal cells 15-20 μm x 5-11 μm, elongated, with four processes, three of these connected to neighboring cells, the fourth one free, long, slightly bent assymmetrically pointing outward; inner cells 8-14 μm x 4-8 μm; cell wall granulated or smooth (Photomicrographs of the Freshwater Algae, vol.15, 1995).
Similar species -->> P. boryanum
P. asymmetricum
Shikinawa-ike
Fukuoka, 2001
P. asymmetricum
μm
Saiko 2
Toda
Saitama, 2007
