| Summary: | Thin filamentous cyanobacteria identified by morphology as Leptolyngbya and Phormidium are common in Antarctic biotopes, ranging from microbial mats in lakes and seepages to terrestrial biofilms and crusts. Due to their morphological simplicity, a large number of species were described but the genetic basis of these taxa is largely unknown. The litterature shows that these genera are polyphyletic and that they need detailled revisions.The isolation of strains in unialgal cultures is the first step of an asssessment of the real diversity of these genera. Here we describe the molecular analysis of Antarctic Leptolyngbya antarctica, L. cf fragilis, L. glacialis and Phormidium priestleyi using sequences of different taxonomic markers, the 16S rRNA gene, the ITS and the rpoC1 gene. They appear distributed into four lineages. The phylogenetic tree supports the transfer of certain Phormidium priestleyi strains to the genus Phormidesmis. Similarly, some L. antarctica clearly belong to the new genus Nodosilinea. CCAMBIO
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