Pinnularia is a genus of fresh water algae, more specifically a type of diatom.

[1] Pinnularia is a predominantly fresh-water algae usually found in ponds and moist soil.

A large central vacuole is present with the nucleus suspended in its centre by a transverse cytoplasmic bridge.

One or two pyrenoids are usually present in each chloroplast, although like many heterokont algae, Pinnularia tend to store their energy as fat.

With subsequent generations, the average cell size of a Pinnularia population gradually becomes smaller.