Communities of class Lemnetea minoris O. Bolόs ex Masclans 1955on territory of National Nature Park “Pyryatynsky”

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Introduction. National Nature Park “Pyryatynsky” is a valuable reserve of flora and vegetation of the Left-Bank Dniepro. The extensive hydrological network of the Udai River and the wide representation within this nature reserve of floodplain reservoirs are the reason for the high diversity of plant communities of higher aquatic vegetation. Fragmentary and non-comlete information about this type of vegetation are existed in literature, however, without geobotanical releves and detailed characteristics of the structure of phytoceonoses, synecology and synchorology. In this article we classified the communities of free-floating vegetation of NPP Pyryatynsky and identify the features of their syntaxonomic and ecological differentiation. Purpose . To study phytocenoses of the class Lemnetea minoris, to classify communities, to describe features of structure and their distribution on the investigated territory. Methods . The description of communities was carried out within their natural boundaries. The flow of reservoirs was determined by the scale of D.V. Dubyna. The projective coating was fixed as a percentage with subsequent transformation into scores of the modified scale B.M. Mirkin. In total, 107 geobotanical releves were performed during the period 2010–2017. Treatment of fitosociological data was performed with the JUICE software package. The nomenclature of syntaxons was consistent with the International Code of Phytosociological Nomenclature (ICFN). Results . The class Lemnetea is represented by 3 orders, 4 alliances and 11 associations on the territory of NPP Pyryatynsky. The order Lemnetalia minoris have highest level of phytocenotic diversity, most of the phytocenoses of which are the typical for the higher aquatic vegetation of the Udai River, its tributaries and outside floodplain reservoirs. At the same time, rare and little-studied in the region associations Lemnetum gibbae Miyawaki et J. Tuxen 1960 and Lemno gibbae – Wolffietum arrhizae Slavnic 1956 were found. The order Ceratophyllo – Hydrocharietalia morsus-ranae unites communities of unrooted pleistophytes and gidatophytes that develop in eutrophic low-flowing or closed reservoirs with silty bottom sediments and a significant admixture of detritus with neutral reaction of medium. The order Utricularietalia is represented within the NNP by one association, which occurs infrequently and quickly disappears from the marked localities under the influence of successional processes and disturbances of the Udai river basin due to climate change and anthropogenic pressure. Originality . This is first prodrome of class Lemnetea minoris for territory of National Nature Park “Pyryatynsky”. All obtained results based on original field data. Conclusions. The class Lemnetea is well-presented on territory of National Nature Park “Pyryatynsky”. It represented by 3 orders, 4 alliances and 11 associations. The order Lemnetalia minoris have highest level of phytocenotic diversity and includes rare communities Lemno gibbae – Wolffietum arrhizae and Lemnetum gibbae. Communities of order The order Utricularietalia need protection, because occurs infrequently and quickly disappears from the marked.