Pinnularia, like most diatoms, can reproduce by simple cell division. Nuclear division occurs by mitosis and cell divides into two parts. Each daughter receives one of the parent cell's thecae, which becomes that cell's epitheca.
Pinnularia reproduces via basic cell splitting, a process similar to that found in other diatoms. During this process, mitosis occurs, resulting in two identical daughter cells. Each new cell receives one of the parent's thecal layers, which becomes its own epithecal layer.