New association Cladophoro fractae-Stuckenietum chakassiensis of the class Ruppietea maritimae from Siberia
New ass. Cladophoro fractae-Stuckenietum chakassiensis Kipriyanova ass. nov. hoc loco, referred to the alliance Cladophoro fractae-Stuckenion chakassiensis Kipriyanova all. nov. hoc loco, to the order Ruppietalia maritimae J. Tx. ex Den Hartog et Segal 1964 and to the class Ruppietea maritimae J. Tx. ex Den Hartog et Segal 1964 was described in Siberia. Nomenclature type (holotypus) - relevé 3 (author''s number 5.3) in Table. Dominating diagnostic species is Stuckenia chakassiensis (Kaschina) Klinkova (Flora Nizhnego Povolzhiya, 2006). (Synonyms are Potamogeton pectinatus L. subsp. chakassiensis Kaschina in Krasnob. et Safonova, 1986, Novoe o Fl. Sibiri : 245. - P chakassiensis (Kaschina) Volob. 1991, Sibir. Biol. Zhurn. 5 : 75. - P chakassiensis var. tenuior Volob. 1993, Sibir. Biol. Zhurn. 3 : 57. - P intramongolicus Ma, 1983, Acta Bot. Bor.-Occid. Sin. 3(1): 8, nom. inval. - P acifolius Ma, 1983, Acta Bot. Bor.-Occid. Sin. 3(1): 8, nom. inval. - Stuckenia intra-mongolica (Ma) Tzvel. 1999, Bot. Zhurn. 84(7): 111, nom. illeg.). The species richness (data of fifteen relevés) is 1-4 per relevé, which is explained by relatively high salinity values. A total of 8 species were registered in association communities. Communities with total cover 20-95 %, occupy quite large (from 20 to more than 100 m<sup>2</sup>) areas in the studied lakes. The main layer - submerged plants - is made by shoots of Stuckenia chakassiensis. There are other species with a wide range of halotolerance (Cladophora species), as well as brackish and saline water species (Ruppia maritima, Chara aspera, C. canescens, C. altaica) and Althenia orientalis, Ruppia drepanensis, R. cirrhosa, Lamprotamnium papulosum, which are much rarer in Western Siberia. Other layers are not expressed, except for the emergent plants represented by reed on the border of belts of submergent and emergent vegetation. Communities of associations were observed only in the brackish (oligohaline, mesohaline, polyhaline) waters of the various classes and groups: mainly sodium-chloride in the south of West Siberia, and sodium-bicarbonate in East Siberia. Not too often they were found in sodium-sulfate and magnesium-bicarbonate waters. Salinity range of association in Transbaikalia was 1.11-9.57 g/dm<sup>3</sup>. Maximum salinity for Stuckenia chakassiensis communities in the Novosibirsk region was 10.32 g/dm<sup>3</sup>, in the lakes of Khakassia - 28.8 g/dm<sup>3</sup>. The pH values varied from 6.55 to 10.50. Special publications (Kipriyanova et al., 2016, 2017) are devoted to a description of the hydrochemical preferences of the S. chakassiensis and some other species of the genus Stuckenia in the lakes of Transbaikalia. According to the obtained data in the brackish waters of the lakes of East Siberia, S. chakassiensis forms thickets with rather high productivity (up to 517.4±89.51 g/m<sup>2</sup> abs. dry weight) (Kipriyanova et al., 2017). The association''s area of distribution appears to coincide with the range of the species, which is a southern part of Siberia (Kurgan Region, Novosibirsk Region, Altai Territory, the Republic of Khakassia, the Republic of Buryatia, Trans-Baikal Territory), northern Kazakhstan, northern China, Mongolia, and rarely - the South Eastern Europe: Volgograd Region (Chernyshkovsky district, in the estuaries and lakes of the Tsimlyansky sand massif near the hamlets Tormosin and Morskoy ) (Flora of the Lower Volga region, 2006; Krasnaya..., 2006) and in the Caucasus (Tzvelev, 1990). The association quite logically fits into the class Ruppietea and the order Ruppietalia. In addition to the actual cenoses of different Ruppia species, the communities of other aquatic halotolerant plants, such as the association of emergent plant Eleocharitetum parvulae (Christiansen 1934) Gillner 1960, the bryophyte cenoses Rielletum helicophyllae Cirujano et al. 1993, Rielletum notarisii Cirujano et al. 1993 may be included into this class (Rivas-Martmez et al., 2002; and othe