Gomphonema parvulum is smaller (10–36 μm long) with less strongly radiate striae. Gomphonema gracile lacks protracted apices and also has more weakly radiate striae. Valves of Gomphonema mexicanum are larger and lack the protracted headpole.
LM scalebar = 10 µm
Length Range
24-50 µm
Width Range
6.9-8.5 µm
Striae in 10 µm
9-12 at the valve center, 14-18 near the apices