Pinnularia torta also has large, linear valves and a asymmetric axial area. Pinnularia torta is smaller, with a more linear central valve and ends, finer striae and more asymmetric axial area.
Pinnularia flexuosa has linear valves, with straight sides and less radiate striae in the central valve.
Pinnularia ectorii has a more expanded central valve; the valves are not as linear.