The microflora of hypogean environments has been studied increasingly worldwide. However, some sites have hardly been examined or not studied at all; this is the case for the Giant Cave, a Karst show cave located near Trieste, Italy. In the present study we began characterizing the Giant Cave Lampenflora by using a polyphasic approach, focusing, in particular, on three Leptolyngbya-like strains named GR2, GR4, and GR13. Light and electron microscopic observations were carried out and the water-soluble pigment composition was analysed. Phylogenetic reconstruction, based on the 16S rRNA gene and the 16S-23S ITS region, was performed to better understand the taxonomic position of these strains, complemented by 16S-23S ITS secondary structure analysis. Ecological and geographical data for the investigated strains and for the other cyanobacterial strains grouping with them in the phylogenetic reconstructions were also considered. Based on the results, strain GR2 was ascribed to the species Heteroleibl...

Cyanobacteria (phylum Cyanophyta/Cyanobacteria, class Cyanophyceae) are among the most widespread organisms and are able to adapt themselves to different extreme environments. These micro‐organisms have an important ecological role, given their ability to perform oxygenic photosynthesis, and are employed in different fields based on their ability to produce several bioactive compounds. Their prokaryotic nature, the presence of many cryptic species, and the coexistence of different nomenclature systems make the taxonomic identification of cyanobacteria particularly difficult. Moreover, for several species, the original reference strains (holotypes) are lacking. Increasingly, authors are using a polyphasic approach to characterize cyanobacteria, while typification is a recent trend that is being used to solve the problem of missing holotypes in other micro‐organisms. Here we focus on a filamentous cyanobacterium, isolated from the Euganean Thermal District (Padova, Italy) and temporarily named strain ETS‐02, using a polyphasic approach that includes morphological, ultrastructural, biochemical (pigment and fatty acid content), physiological (nitrogen fixation), and genetic (16S rRNA, 16S–23S ITS, cpcB‐IGS‐cpcA, rpoC1, gyrB, rbcL, nifD loci) analyses. The description of Phormidium cf. irriguum CCALA 759 as the epitype of Phormidium irriguum was also used to complete the characterization of strain ETS‐02.