The taxonomic validation of the cyanobacterial genus Halothece

In 1998, Garcia-Pichel and coworkers studied 13 strains of extremely halotolerant, unicellular cyanobacteria. One strain, which was isolated from a coastal salty habitat in Baja California, Mexico, was found to represent a genetically distinct subcluster, different from another related coherent group of 12 morphologically similar types. This subcluster was designated as 'true Halothece', in comparison with 'Euhalothece' strains. The genetic characters clearly indicated their separation of Halothece at the generic level (less than 91% of genetic similarity), but the formal description, corresponding with bacteriological or botanical nomenclatoric rules, was never published. The present article comprises the valid description of the genus Halothece based on the type strain MPI 96P605, supported by new original studies of the morphological, ecophysiological and ultrastructural variability of the type strain.