When cells that are within the filament die, the wall tends to become weakened, and the filament fragments. This latter is a form of asexual reproduction. A specialized case of this form of fragmentation is characterized by Aphanizomenon in which fragmentation occurs in a cell adjacent to a median located heterocyst in a filament. It should be noted that Aphanizomenon is a colony of loosely adhering filaments each of which has tapered and clear terminal cells and an intercalary heterocyst, generally located in the middle of the filament. The presence of false branching is a characteristic of the family Scytonemataceae, and is evident in the genus Scytonema .
False branches arise interior to the filament as follows.
An interior cell dies. The adjacent cells begin active cell division, and the new growth erupts through the outer sheath of the filament. False branching in Scytonema occurs in pairs. Calothrix also has false branching. True branching is found in the order Stigonematales.