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Two isolates of Oculatella from biological soil crusts in the arid and semi–arid tropical upland region of México were characterized using a polyphasic approach which included morphology, ecology, 16S rRNA and 16S–23S ITS phylogenetic analysis, percent identity of 16S rRNA gene sequence, percent dissimilarity of 16S–23S ITS sequence, and secondary structure of conserved ITS domains. The two species shared the generic synapomorphy of a reddish granule at the tip of mature apical cells, and possessed a single ribosomal

operon with both tRNA genes (tRNAIle and tRNAAla) based upon our analysis and the analysis of the other spe- cies in the genus. After characterization, the strains were compared with 10 previously described and similarly

characterized species in the genus, and based upon the evidence obtained, the strains were described as two new species, O. dilatativagina and O. leona. O. dilatativagina has an extensively widened sheath, and thus is morphologically separated from all other taxa described thus far. O. leona is morphologically highly similar to soil species found in North and South America, and should be considered a cryptic species among these taxa. The recently developed criterion for species recognition using percent dissimilarity among ITS gene sequences in orthologous ribosomal operons was found to be effective in separating cryptic species of Oculatella, and has consistently been useful and sufficient for separation of closely related species in other cyanobacterial genera.

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