Section [ Calocylindrus ]: Cell body cylindrical, slightly constricted at the center,cell surface granulated or with knobs.
Species [ var. amoenum ]: Cell body cylindroid, 42-67 μm long, (22-28)-30 μm wide, L/W=2, isthmus 13-21 μm wide; cell wall covered with large granules, longitudinally arranging in 7-8 rows forming a cross (+) pattern on the cell wall; 2 pyrenoids in each semicell.
[ var. alternans ]: Cell body 44-45 μm long, 23-24 μm wide, isthmus 15.4 μm wide; granules arranging as an "X"-shaped pattern on the cell wall (Illustrations of The Japanese Fresh-water Algae, 1977).
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Similar species -->> C. pseudoamoenum;
C. amoenum
v. amoenum
43 x 20 μm
Tashirodaira m.5
Hakkoda mountain
Aomori, 2006
C. amoenum
v. amoenum
46 x μm
Omine numa
Tsukiyono
Gunma, 2003
C. amoenum
v. amoenum
50 x 23 μm
Omine numa
Minakami
Gunma, 2007.4
C. amoenum
v. amoenum
μm
Omine numa 5
Minakami
Gunma, 2007.10
C. amoenum
v. amoenum
45-47 x 24-25 μm
Shimo-no-koike
Shiga highland
Nagano, 2004
C. amoenum
v. amoenum
49 x 25 μm
Shimo-no-koike
Shiga highland
Nagano, 2006
C. amoenum
v. amoenum ?
39 x 21 μm
44 x 24 μm
Shimo-no-koike
Shiga highland
Nagano, 2004
C. amoenum
v. amoenum ?
50 x 25 μm
Shimo-no-koike
Shiga highland
Nagano, 2005
C. amoenum
v. alternans ?
43 x 25 μm
Shimo-no-koike
Shiga highland
Nagano, 2005
C. amoenum
v. amoenum ?
45 x 24 μm
Miyatoko m.5
Minami-Aizu
Fukushima, 2008