A set of thirty Calothrix strains, isolated from diverse geographical regions of India, were characterised using morphological and physiological attributes. Significant differences were observed among the Calothrix strains with regard to the shape and size of trichomes and individual cells within a filament, besides the activities of the enzymes involved in nitrogen metabolism. Informative morphological and physiochemical characters have been identified that could aid in differentiation and utilisation of Calothrix strains as bioinoculants or as sources of pigments.