At the small end of the size range, N. innominata, N. soratensis and N. inconspicua may be difficult to distinguish. Nitzschia soratensis is more elliptic, areolae may be visible in LM and the striae are arched near the apices. Nitzschia inconspicua has more apiculate ends. Nitzschia fonticuloides has fine striae and subrostrate apices. Nitzschia frustulum has linear valves, with parallel parallel to lanceolate margins. The apices of N. frustulum are pointed to narrowly rounded.
BioData Reference
Krammer and Lange-Bertalot 2/2 Pl 68 Fig 1-8