Systematic position
Class-Cyanobacteria
Order-Nostocales
Family-Scytonemataceae
Genus-Scytonema
The algae grow epiphytically commonly on wet barks just after rains. It is also found growing on wet rocks or walls appearing as black cotton patches. Nearly fifty species of the alga have been reported from India. The thallus consists of filaments with distinct apical and basal regions. The sheath of the filament may be colored or hyaline. The genus is characterized by the presence of heterocyst's and germinate kind of pseudo branching. The false branching arises laterally because of the degeneration of an intercalary cell. In many species, the intercalary growth of trichome exerts great pressure to the sheath which eventually ruptures. With the result, a loop is formed outside the trichome. The branches continue their growth out of the loop. Sometimes, pseudo branching are also produced by degeneration of heterocyst's followed by the growth of the two filaments on either sides. The cells may be oval, quadratic or cylindrical or as long as broad. Besides heterocyst's, hormogonia are frequently formed during reproduction. Scytonema are capable of nitrogen fixation from the atmosphere and thus it increases the nitrogen content of the soil.
