Diversity of aquatic vegetation (Lemnetea O. de Bolòs et Masclans, Potamogetonetea Klika in Klika et Novák 1941) in the Russian Federation

In a frame of the project “Vegetation classificati on of Russia”, we have compiled the prodromus of two classes of aq uatic vegetation, i.e. Lemnetea O. de Bolòs et Masclans 1955 and Potamogetonetea Klika in Klika et Novák. The diversity of Lemnetea in the Russian Federation is consists of 15 associations belonging to 3 alliance s and one order. Diversity of Potamogetonetea is presented by 56 associations from 5 alliances and two orders. The presented version of the prodromus is a preliminary. We count all valid sytaxa revealed fro m the territory of the Russian Fedeeeration. The final prodromus will be ob tained after the numerical data processing and considering the plura lity of syntaxonomic decisions. The project “Vegetation classification of Russia” l unched in 2020 aims to inventory the plant community diversity of the Russian Federation and elaborate the entire classification of its vegetation [1]. At the first stage, it is ne cessary to collect all available information already known about the vegetation diversity of the target territory. For this purpose, we have compiled the prodromus of aquatic vegetation r evealed in the Russian Federation. This paper presents the complete hierarchy of valid ly published syntaxa belonging to classes Lemnetea O. de Bolòs et Masclans 1955 and Potamogetonetea Klika in Klika et Novák. Material and methods We follow the ecological-floristic approach of phyt osociology, also known as the BraunBlanquet approach [2, 3], whose nomenclature is reg ulating by the International Code of Phytosociological Nomenclature [4]. At the highest levels of hierarchy, we follow the nomenclature of the EuroVegChecklist [5]. The nomen clature of association names was checked after the contemporary phytosociological li terature. For the last purpose, the monograph on the aquatic and wetland vegetation of the Czech Republic [6] was especially * Corresponding author: lkipriyanova@mail.ru © The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/). BIO Web of Conferences 38, 00057 (2021) Northern Asia Plant Diversity 2021 https://doi.org/10.1051/bioconf/20213800057

The project "Vegetation classification of Russia" launched in 2020 aims to inventory the plant community diversity of the Russian Federation and elaborate the entire classification of its vegetation [1]. At the first stage, it is necessary to collect all available information already known about the vegetation diversity of the target territory. For this purpose, we have compiled the prodromus of aquatic vegetation revealed in the Russian Federation. This paper presents the complete hierarchy of validly published syntaxa belonging to classes Lemnetea O. de Bolòs et Masclans 1955 and Potamogetonetea Klika in Klika et Novák.

Material and methods
We follow the ecological-floristic approach of phytosociology, also known as the Braun-Blanquet approach [2,3], whose nomenclature is regulating by the International Code of Phytosociological Nomenclature [4]. At the highest levels of hierarchy, we follow the nomenclature of the EuroVegChecklist [5]. The nomenclature of association names was checked after the contemporary phytosociological literature. For the last purpose, the monograph on the aquatic and wetland vegetation of the Czech Republic [6] was especially useful. Assignment of plant communities to the concrete association was conducted following such criteria as dominancy, physiognomy, and belonging to a particular functional group of aquatic plants [6,7].
Despite the practice by some Russian phytosociologists to use the shorter form of syntaxa names derived from the genus Potamogeton (Potametea, Potametalia, Potamion), we agree with arguments by authors of the EuroVegChecklist [5], while applying the full name of the genus (i.e. Potamogetonetea, Potamogetonetalia, Potamogetonion).

Results and Discussion
Although aquatic plant communities have a simple structure, many points complicate their classification: i.e. general floristic poverty, ecological and morphological plasticity of aquatic and wetland plants, insufficient taxonomic knowledge in some groups of plants, various concomitant species by the same dominant in different environmental conditions [18]. Besides that, there are various association concepts for species-poor vegetation: i.e. broad associations (synthetic concept), one dominant species -one association (pragmatic concept), and narrowly defined associations (splitting concept) [7,19]. Additionally, it is not evident if to treat stands of interspecific hybrids as distinct associations?
According to the EuroVegChecklist [ [10,15]. However, the mentioned species prefer shallow waters and shoals. Therefore, we consider these community types have to be placed into the class Littorelletea uniflorae Br.-Bl. et Tüxen ex Westhoff et al. 1946.
Below, we present the prodromus of Lemnetea and Potamogetonetea registered on the territory of the Russian Federation. As the first approximation, we do not adhere strictly to any association concepts noted above; we instead count all valid syntaxa revealed on the territory of the Russian Federation. The solution, which association concept should be applied, will be made later, after the numerical data processing and considering the plurality of syntaxonomic decisions [21]. Ecological peculiarities of plant communities, the presence of stable combinations of diagnostic taxa, and their vicariant combinations in longitudinal sectors of Northern Eurasia will also be considered. The presented version of the prodromus is a preliminary view of Lemnetea and Potamogetonetea diversity within the vast territory of the Russian Federation. We appreciate any additions and comments from the readers.