Fragilariforma constrica f. stricta is smaller and lacks undulate margins. Fragilariforma constricta var. trinodis and Fragilariforma polygonata have tri-undulate margins. Fragilariforma hungarica var. tumida has a single, large central undulation.

LM scalebar = 10 µm
Fragilaria constricta LM5 Fragilaria constricta LM7 Fragilaria constricta LM6 Fragilaria constricta LM4 Fragilaria constricta LM3 Fragilaria constricta LM1 Fragilaria constricta LM2
Length Range
22-40 µm
Width Range
3.7-5.9 µm
Striae in 10 µm

Fragilariforma polygonata

(A.Cleve) Kingston, Sherwood and Bengtsson 2001

Fragilariforma polygonata LM3 Fragilariforma polygonata LM2 Fragilariforma polygonata LM1 Fragilariforma polygonata LM5 Fragilariforma polygonata LM4
Length Range
22.1-30.2 µm
Width Range
9.8-10.5 µm
Striae in 10 µm

Also compare to

Fragilariforma constricta f. stricta

(A.Cleve) Poulin in Hamilton

Fragilariforma constricta var. trinodis

(Hust.) Hamilton

Fragilariforma hungarica var. tumida

(A.Cleve) Hamilton