Features of Sexual Reproduction and Mating System of <i>Ulnaria acus</i> (Bacillariophyta)
Sexual reproduction and mating system of the freshwater diatom Ulnaria acus (Bacillariophyta) was described for the first time. Mating system of the species includes, apparently, only heterothallic way of reproduction: during the three-year observation period neither male nor female clones have shown the ability to reproduce homothallically. The type of sexual reproduction is cis-anisogamous; in many details it similar with reproduction of closely related species Ulnaria ulna, Tabularia fasciculata, and Tabularia tabulata.