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: Colonies of 8-32 (rarely 4, 64 or 128 cells) with large intercellular space; inner cells H or X-shaped, trapezoid to rectangular when matured; outer half of the marginal cells prolonged into two horn-like processes with a tuft of long bristles; daughter colonies formed in a vesicle released from mother cell; cell wall smooth (Photomicrographs of the fresh-water algae, 1994).
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Similar species -->> P. angertiniense
var. duplex - var. reticulatum Space present at the center of colonies 
var. duplex
32-cells
32 = 16+11+5
Japan, 1997
var. duplex
16-cells
16 = 11+5
Japan, 1998
var. duplex
16-cells
16 = 11+5
Uruguay, 1999
var. duplex
16-cells
16 = 11+5
near Town Hall
Shobu
Saitama, 2004
var. reticulatum ?
32-, 16-cells
32 = 16+11+5
Japan, 1998
