Abstract
In the course of study of the cyanobacterial flora of Ethiopian soil crusts, we isolated a distinctive strain most closely resembling Chroococcidiopsis kashayi, and at first considered it to be a new Chroococcidiopsis species. However, when placed in nitrogen-free medium for an extended time period this strain developed heterocytes, and consequently was placed in the genus Nostoc. It is morphologically distinct from all other Nostoc species due to its consistent formation of microscopic few-celled colonies lacking clear filamentous organization, which release smaller colonies from the mother colony, leaving behind a persistent thin firm sheath that resembles cell wall material in the light microscope. Analysis of 16S rRNA and 16S-23S ITS sequence data confirmed its uniqueness among numerous strains of soil Nostoc. We are describing it as Nostoc oromo, named for the nationality of the people from the region of its origin.