Lychnothamnus barbatus (Meyen) Leonhardi 1863, A New Species to the Flora of Montenegro

This study presents a newly discovered site of Lychnothamnus barbatus, one of the rarest charophytes worldwide of a disjunctive, Euro-Australasian-American distribution. The species is the only representative of the genus Lychnothamnus on a global scale, hence its threat poses a risk of extinction to the entire lineage. In June 2019, Lychnothamnus barbatus was discovered in Lake Malo Blato, a north-western bay of Lake Shkodra/Skadar, to be a new element to the flora of Montenegro. Lychnothamnus barbatus was recorded at a depth of 3 m, in nutrient-poor but calcium-rich water and on a muddy substrate in the zone of submerged vegetation composed of charophytes and angiosperms. The collected thalli of L. barbatus were young and sterile, green, slightly calcified, and up to 15 cm high. Except for gametangia, all features which are diagnostic for this rare charophyte were well developed. Based on the synthesis of the current state of knowledge, the new site of L. barbatus is presented in the context of the species’ ecological requirements and climatic plasticity, current distribution, and history in the Balkans. •A new site of a worldwide rare charophyte was discovered in the Balkans.•Lychnothamnus barbatus is a new species to the flora of Montenegro.•The species occurs in nutrient-poor but calcium-rich water and on a 3 m deep muddy substrate.•The history of Lychnothamnus in the Balkans dates back to the Miocene.