Branched filamentous cyanobacteria develop the most complex morphology of all procaryotes. Of these Stigonema is at the apex with multiseriate branches, akinetes and heterocysts.

The relationships and boundaries between the genera Hapalosiphon, Fischerella and Stigonema are poorly defined (Hindak 2012).

Hindak, F. 2012. Hormogonia in two nostocalean cyanophytes (cyanobacteria) from the genera Hapalosiphon and Fischerella. Biologia 67(6): 1075-1079.