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

The genus Klebsormidium 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 Klebsormidium an important object for phycological research. To advance the molecular phylogeny of Klebsormidium, 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 rbcL and concatenated ITS2-rbcL fragments. The accuracy of these methods was further validated against molecular, morphological, and ecological data. According to an integrative approach, Klebsormidium mirabile sp. nov. 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 Klebsormidium is a potential source of polyunsaturated fatty acids, including linoleic, α-linolenic, and hexadecatrienoic acids.