Species delimitation in the genus Klebsormidium (Klebsormidiophyceae, Charophyta), including description of Klebsormidium mirabile sp. nov. with high content of polyunsaturated fatty acids

The genus <i>Klebsormidium</i> is a cosmopolitan filamentous alga that belongs to the phylum Charophyta and inhabits a wide range of environments, primarily freshwater, soil, and aerial habitats. Its basal position on the Streptophyta phylogenetic tree, widespread distribution and significant functional role make the genus <i>Klebsormidium</i> an important object for phycological research. To advance the molecular phylogeny of <i>Klebsormidium</i>, we conducted the first comparative evaluation of six species delimitation methods - ASAP (Assemble Species by Automatic Partitioning), LocMin (Local Minima), KoT (K over Theta), GMYC (Generalized mixed Yule-coalescent), mlPTP (Poisson Tree Process with Maximum Likelihood), and bPTP (Poisson Tree Process with Bayesian inference) - using <i>rbc</i>L and concatenated ITS2-<i>rbc</i>L fragments. The accuracy of these methods was further validated against molecular, morphological, and ecological data. According to an integrative approach, <i>Klebsormidium mirabile</i> <b>sp. nov.</b> was proposed as a new charophyte species from soil of the Fergana Valley, Uzbekistan. In addition, a study on the fatty acid composition showed that the authentic strain VKM Al-436 of this new species of <i>Klebsormidium</i> is a potential source of polyunsaturated fatty acids, including linoleic, α-linolenic, and hexadecatrienoic acids.