Integrative taxonomy of a new Odontidium (Tabellariaceae) species from Poland: Combined morphological and molecular evidence

Mountain springs are important ecosystems for freshwater biodiversity and may serve as refugia for previously unrecognised diatom diversity. During investigations of springs in the Bieszczady National Park (Poland), a morphologically distinctive taxon of the genus Odontidium was observed, which is described here as Odontidium fontinale Sulkowska, Żelazna-Wieczorek, Olszyński & Wetzel, sp. nov . A morphological and morphometric description was prepared based on analyses conducted using light and scanning electron microscopy. The new species was compared with morphologically similar taxa, including Odontidium mesodon , O. minutum , O. rostratum , and Tetracyclus rupestre . Odontidium fontinale sp. nov . is distinguished primarily by its small valve dimensions and a relatively low density of transapical ribs. Furthermore, despite its frequent occurrence in mountain freshwater habitats, the genus Odontidium remains poorly known at the molecular level. To address this, molecular data based on rbc L sequences from cultures of the new species were obtained to assess its phylogenetic position.