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Planothidium frequentissimum differs from other Planothidium species with a cavum, such as P. biporomum and P. potapovae, by the lanceolate to elliptical valves with rounded or slightly drawn-out apices. The raphe valves of lanceolate shape may not be distinguishable from those of P. lanceolatum. The rapheless valves, however, of P. frequentissimum possess a cavum – a feature not found in P. lanceolatum.

LM scalebar = 10 µm
Gs119780 1 Ed Planothidium frequentissimum LM3 Planothidium frequentissimum LM2 Mo000019 1A Ed 5 Planothidium frequentissimum LM1 Gs181995 1B Ed Mo000019  Plfreq 1B Ed
Length Range
5-17 µm
Width Range
3-6 µm
Striae in 10 µm
13-18

Planothidium potapovae

C.E.Wetzel and Ector 2019

Gsn23403  Plrostr 3 Gsn23403  Plrostr 2 Gsn23403  Plrostr 5 Gc48893A 1A
Length Range
11.0-17.5 µm
Width Range
5.0-6.0 µm
Striae in 10 µm
11-13

Planothidium biporomum

(M.H.Hohn and Hellerman) Lange-Bert. 1999

Planothidium bipororum LM3 Planothidium bipororum LM1 Planothidium bipororum LM4
Length Range
12-25 µm
Width Range
5.4-7.0 µm
Striae in 10 µm
12-15

Planothidium lanceolatum

(Bréb. ex Kütz.) Lange-Bert. 1999

De000084 6 De000084 4 De000084 7 Ih042040  Pllanc2 Ih042040  Pllanc4 Ih042040  Pllanc1 Mo000019 1
Length Range
7-24 µm
Width Range
4.5-8.0 µm
Striae in 10 µm
12-15

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