Pluricentimetric colonies of Nostoc parmelioides exhibit two types of calcifications: (1) rhombs, either isolated, chains, or grouped in elongate masses around sheathless trichomes in the interior of the colony; or (2) discs with fibroradiating and concentric fabric, in which radial elements are elongate, stacked, upside-down, bell-shaped monocrystals, with concentric laminations in cross section. The discs could be the result of a very peculiar calcification of an epiphytic organism, probably a bacterium. These structures can be referred to as bacterial microstromatolites.