Charophytes (Charales, Characeae) of the Altai Mountains, a hotspot for charophytes in North Asia

A checklist of charophytes for the Altai Mountains region of Kazakhstan and Russia was compiled based on field studies conducted from 1995 to 2023, evaluation of available voucher specimens collected from 1826 to 2020, and a critical assessment of published records. In total, we recognized 28 species from five genera (16 Chara , eight Nitella , one Nitellopsis , one Sphaerochara , and two Tolypella species) across 83 sites. This level of charophyte species richness is among the highest in the Palearctic, higher than any neighboring areas. This diversity, however, is threatened by the rapid development of tourist infrastructure and recreation in the region. The Altai Mountains are one of the few important areas for Chara strigosa A. Braun and C. spinosa-vaillantii Rupr., harboring stable populations that did not require protection in Asia. Large oligotrophic lakes of North Asia have low species richness of charophytes and no peculiar species, but can support large stands of a few charophyte species. We identify important charophyte sites based on species richness, the presence of rare species, and the stability of populations. Additional surveys of charophytes of the Altai Mountains are warranted, not only in Kazakhstan and Russia, but also in Mongolia and China.