Family: Colonies of a fixed number of cells or reticulated bag in shape; chloroplasts plate-like or reticulated, with one or many pyrenoids; asexual reproduction by zoospores, sexual reproduction by fertilization (Illustrations of The Japanese Fresh-water Algae, 1977).
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).

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Two or more horn-like processes; Intercelluar space absent
P. boryanum 37 samples 199?-2006	P. boryanum ? similar to biradiatum 6 samples Uruguay, 1999	P. muticum or P. boryanum v. longicorne 17 samples 128, 64, 16 cells Japan, 1998-2008	P. tetras 44 samples 16, 8, 4 cells 1998-2007
Pediastrum sp. colonies 25 μm φ N/L= megamiyama Nishi-no-miya Hyogo, 2004	P. angulosum 6 samples surface ridged col. μm φ 2001-2006	P. integrum 9 samples col. μm φ Japan, 2002-2007
Two or more horn-like processes; Intercelluar space present
P. duplex var. duplex 21 samples 1997-2006	P. duplex var. reticulatum 8 samples 1997-2005	P. duplex var. gracilimum 19 samples 1997-2004	P. duplex v. rugulosum 9 samples 1997-2005
P. duplex v. rotundatum 5 samples 1997-2001	P. duplex var. reticulatum ? col. μm φ	P. duplex var. reticulatum ? col. μm φ
P. angertiniense 1 sample Uruguay, 1999	P. biradiatum ? 2 samples col. μm φ 1999-2003	Pediastrum sp. 11 samples col. μm φ 1999-2006	Pediastrum sp. col. 35 μm φ Iruma river Kawagoe Saitama, 2004
One horn-like process on each outer cell
P. simplex v. simplex 4 samples 1997-2006	P. simplex v. duodenarium 23 samples 1997-2008	P. simplex v. echinulatum 19 samples 1997-2006	P. asymmetricum col. μm φ 2 samples 2001-2007

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