Compare

Pinnularia undula var. major is larger and its central expansion is smaller than the distal expansion. Pinnularia undula and P. undula var. major both have pronounced markings on the central area. Pinnularia divergens is similar in valve size and outline, but the central area is rhombic and widens to a small fascia, reaching the valve margin.

LM scalebar = 10 µm
Pinnularia decrescens LM3 Pinnularia decrescens LM5 Pinnularia decrescens LM2 Pinnularia decrescens LM1 Pinnularia decrescens LM4 Pinnularia decrescens LM6 Pinnularia decrescens LM7
Length Range
80-93 µm
Width Range
14-17 µm
Striae in 10 µm
9-11

Pinnularia undula

(Schumann) Krammer 2000

Pinnularia undula Pinnularia undula Pinnularia undula Pinnularia undula Pinnularia undula Pinnularia undula
Length Range
63-87 µm
Width Range
15-17 µm
Striae in 10 µm
9-10

Pinnularia undula var. major

(A.W.F.Schmidt) Krammer 2000

Pinnularia undula var. major LM4 Pinnularia undula var. major LM3 Pinnularia undula var. major LM2 Pinnularia undula var. major LM5 Pinnularia undula var. major LM6 Pinnularia undula var. major LM1
Length Range
96-156 µm
Width Range
21-24 µm
Striae in 10 µm
8-11

Also compare to

Pinnularia divergens

BioData Reference
Krammer 2000 Pl 28 Fig 1-6 Pl 29 Fig 1-6