Valves of Pinnularia nodosa var. percapitata are more markedly triundulate, with more distinctly capitate apices. The central undulation of the variety is usually a bit wider than the distal undulations and valves are wider (7.7-10.6 µm). Pinnularia nodosa is distinguished from other Pinnularia species with triundulate margins by the mottled pattern in the axial and central areas.