Species [ var. minutum ]: Cell body cylindrical, 50-230 μm long, 7-18 μm wide, L/W=8-12; semicells not swelled at base, slightly tapered, with blunt and smooth ends; cell wall smooth or finely dotted; chloroplasts located along cenral axis, with about 6 laminae; pyrenoids arranged linearly, 3-7 in each semicells.
[ var. elongatum (W. et G.S. West) Cedergren ]: 257-550 μm long, 8-16 μm wide, L/W=28-40;
[ var. crassum (W. West) Krieger ]: Shorter and wider than v. minutum, 40-102 μm long, 12-20 μm wide, L/W=4-5;
[ var. cylindricum (Borge) Krieger ]: 175-300 μm long, 15.5-21 μm wide, L/W=14-15;
[ var. gracile (Wille) Krieger ]: Thinner and longer than v. minutum, 110-240 μm long, 6.5-15 μm wide, L/W=14-20;
[ var. latum Kaiser ]: Wider than v. minutum, 160-352 μm long, 19-28 μm wide, L/W=8-11 (Illustrations of The Japanese Fresh-water Algae, 1977).

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var. minutum: 50-230 μm long, 7-18 μm wide, L/W=8-12
var. minutum 115 x 13 μm L/W=8.8 Sukawa highland Kurikoma mt. Akita, 2007	var. minutum 125 x 13.5 μm L/W=9.3 Hachiman-numa m. Hachimantai Iwate, 2005	var. minutum 104 x 15 μm L/W=6.9 Sensho-ga-hara Shizukuishi Iwate, 2007	var. minutum 129 x 13 μm L/W=9.9 Mida-ga-hara Gassan (mt) Yamagata, 2006
var. minutum 106 x 14 μm L/W= Yahei-daira m.4 Azuma mt. Yamagata, 2007
var. minutum 115,118 x 14 μm L/W=8.2,8.7 Midagahara Tate-yama Toyama, 2006	var. minutum 110 x 14.5 μm L/W=7.6 Watasuge marsh Tsugaike highland Nagano, 2006	var. minutum 133 x 13 μm L/W=10.2 Shimo-no-koike Shiga highland Nagano, 2004	var. minutum 102 x 15 μm L/W=6.8 Tanohara marsh Shiga highland Nagano, 2006
var. minutum 105-136 x 13-16 μm L/W=6.6-10.5 Karakemi marsh Yasaka village Nagano, 2005	var. minutum 119,125 x μm L/W=9.9,10.4 Ushidome-ike Norikura highland Nagano, 2005
var. minutum ? 153 x 18 μm L/W=8.5 Kodanuki marsh Fujinomiya Shizuoka, 2006	var. minutum 115 x 14 μm L/W=8.2 Omotsubo marsh 1 Niimi Okayama, 2006	var. minutum 130, 140 x 12 μm L/W=11-12 Kashibaru m.3 Karatsu Saga, 2006
var. latum: Wide, 160-352 μm long, 19-28 μm wide, L/W=8-11
var. latum ? 346 x 40 μm L/W=8.7 smooth surface Otto-Numa Ibaraki, 2002	var. latum 215 x 20 μm L/W=10.8 Numappara marsh Kuroiso Tochigi, 2003	var. latum 242 x 20 μm L/W=12.1 Numappara m.2 Nasu-shiobara Tochigi, 2007	var. latum 228 x 20 μm L/W=11.4 Numappara m.1 Nasu-shiobara Tochigi, 2007
var. latum 143 x μm L/W= Omine-numa Tsukiyono Gunma, 2003	var. latum 265 x 20 μm L/W=13.3 Tashirodaira m5 Hakkoda mountain Aomori, 2006
var. crassum: Short & wide, 40-102 μm long, 12-20 μm wide, L/W=4-5
var. crassum ? 100 x 14 μm L/W=7.1 Omotsubo marsh Tetta-cho Okayama, 2004	v. crassum 88 x 16.5 μm L/W=5.3 Imou bog Toyohashi Aichi, 2004	v. crassum 80 x 21 μm L/W=3.8 Kuroyachi m.2 Hachimantai Iwate, 2007	v. crassum 80-84 x 21 μm L/W=3.9 Sensho-ga-hara Shizukuishi Iwate, 2007
var. gracile: Thin & long, 110-240 μm long, 6.5-15 μm wide, L/W=14-20
v. gracile 233 x 13 μm L/W= 17.9 1 band-form chl. Japan, 1998	v. gracile 163-228 x 8-11 μm L/W= 17-28 Hiroshima, 1998 Movies	v. gracile 265 x 10 μm L/W=26.5 Kashibaru m.II Karatsu Saga, 2008
var. cylindricum: 175-300 μm long, 15.5-21 μm wide, L/W=14-15
v. cylindricum 300 x 19 μm L/W= 15.8 Oze-ga-hara Katashina Gunma, 2006
misc.:
P. minutum ? or diatom ? 250 x 7 μm L/W= 35.7 Japan, 1998	P. minutum ? or P. trabecula ? 460 x μm L/W= Otsuka-ike Mito Ibaraki, 2003

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