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A freshwater dwelling, tapering, heterocytous cyanobacterium (strain V13) was isolated from an oligotrophic pond in the Shrirampur taluka, Ahmednagar district of Maharashtra in India. Initial morphological examination indicated that strain V13 belonged to the genus Calothrix. Subsequent molecular and phylogenetic assessment based on 16S rRNA gene, led us to describe the freshwater/terrestrial clade of Calothrix strains without terminal hairs as a new genus Dulcicalothrix gen. nov., with the type species Dulcicalothrix necridiiformans sp. nov. (Strain V13) on the basis of the necridia forming ability of the strain. Also, the 16S-23S ITS secondary structure analysis clearly differentiated strain V13 from the other members of the clade. Past studies and the current state of knowledge makes it imperative to separate the groups Calothrix (marine/freshwater Calothrix), Macrochaete and Dulcicalothrix (freshwater/terrestrial Calothrix) into separate genera in accordance with the International Code of Nomenclature for Algae, Fungi and Plants. Robust phylogenetic evidence and previous reports strongly support the re-erection of the family Calotrichaceae distinct from the existing family Rivulariaceae.

Five cyanobacterial strains with Nostoc -like morphology from different localities of the Mazandaran province of Iran were characterized using a polyphasic approach. Three strains clustered within the Aliinostoc clade whereas one each of the remaining two strains clustered within the genera Desmonostoc and Desikacharya . The phylogenetic positioning of all the strains by the bayesian inference, neighbour joining and maximum parsimony methods inferred using 16S rRNA gene indicated them to represent novel species of the genera Aliinostoc , Desmonostoc and Desikacharya . The 16S–23S ITS secondary structure analysis revealed that all five strains under study represented novel species unknown to science. In accordance with the International Code of Nomenclature for algae, fungi and plants we describe three novel species of the genus Aliinostoc and one species each of the genera Desmonostoc and Desikacharya .

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