SINOPSIS

The yellow-green algae belonging to the genera Botrydium and Vaucheria (Xanthophyceae) were studied in the south of the Baikal region from 2011 to 2017. As a result, 375 populations of 15 siphonous xanthophytes from Botrydium (1 species) and Vaucheria (13 species and 1 variety) have been revealed in the 218 localities of the studied region. Botrydium granulatum (Linnaeus) Greville was recorded only once while 374 populations represented the taxa from genus Vaucheria. Most of them (365) were found in situ fertile, with reproductive organs. It allowed identifying them without cultivation. Most of the Vaucheria records (about 80%) are Vaucheria bursata (O. Muller) C. Agardh (125 localities), V. racemosa (Vaucher) de Candolle (77), V. canalicularis (Linnaeus) Christensen (53) and V. frigida (Roth) C. Agardh (32). The rest representatives of Vaucheria met much less frequently. Species V. fontinalis (Linnaeus) Christensen, V. aff. aversa Hassall, V. frigida var. major (Rieth) Wang et Bao, V. alaskana Blum, V. cruciata (Vaucher) de Candolle were found in 9—15 localities. Vaucheria birostris Simons, V. schleicheri de Wildeman, V. prona Christensen, V. taylorii Blum, and V. uncinata Kutz. were recorded in five or less localities. In the south of Baikal region, siphonous xanthophytes occur mainly in aquatic and semiaquatic biotopes; in terrestrial habitats, they were rarely found possibly due to the moderately humid and arid continental climate in the region.