A seldom studied and poorly understood feature of cyanobacterial growth and development is the formation of ordered macroscopic structures from microscopic cells, trichomes, and filaments. The forms range from nostoc balls and layered mats of comparatively simple structure to more complex erect tree-like (dendroid) macro-structures. Using macrophotography, time lapse micro-cinematography, light and scanning electron microscopy of Nostoc species in pure culture, it has been possible to show how motility, adhesion and aggregation of photo-induced motile trichomes (hormogonia) result in the macro-morphogenesis of dendroid forms.

Nostocacean development proceeds by the differentiation of cells in a cyclic sequence of stages including: long chains of cells in heterocystous filaments, motile hormogonia, and large rounded cells termed the aseriate phase. When grown from localized inocula on solid media, sequential development recycles across the agar surface of the culture. Different strains and species vary in the form and duration of each stage and the photo-response of hormogonia.