Hormogonia are motile filaments of cells generated by certain Nostocales and Stigonematales cyanobacteria.
When exposed to environmental stress or placed in novel conditions, cyanobacteria differentiate into hormogonia.
Hormogonium differentiation is critical for the establishment of nitrogen-fixing plant cyanobacteria symbioses, particularly those between Nostoc cyanobacteria and their hosts.
Hormogonia are motile fibers. It is shaped at the hour of vegetative multiplication in filamentous cyanobacteria.