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's reproductive method involves straightforward cell division, a characteristic shared with most other diatoms. This process, involving mitotic nuclear division, results in two daughter cells that inherit one of the parent's thecal layers, becoming their own epithecal layer.