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The size range of P. holstii overlaps with P. apiculatum, but these taxa are distinct in several features. The apices are much more narrow in P. apiculatum. Furthermore, the striae of the raphe valve are more radiate. The rapheless valve of P. holstii lacks a cavum, which is present in P. apiculatum.

LM scalebar = 10 µm
Planothidium holstii LM6 Planothidium holstii LM4 Planothidium holstii LM1 Planothidium holstii LM2 Planothidium holstii LM7 Planothidium holstii LM3 Planothidium holstii LM5
Length Range
18-28 µm
Width Range
8-10 µm
Striae in 10 µm
12-16

Planothidium apiculatum

(R.M.Patrick) Lange-Bert. 1999

Planothidium apiculatum LM3 Planothidium apiculatum LM1 Planothidium apiculatum LM4 Planothidium apiculatum LM6 Planothidium apiculatum LM2 Planothidium apiculatum LM5 Planothidium apiculatum LM7
Length Range
25-31 µm
Width Range
9.0-12.7 µm
Striae in 10 µm
10-12