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The increasing impact of anthropogenic factors and climate change affect the growth of a number of taxa of hybrid nature. These taxa are widespread among various taxonomic groups of aquatic and semi-aquatic plants. The genus Sparganium L. В is not an exception. In that regard, the aim of this study is to conduct biomorphological investigation of Sparganium × longifolium Turcz. ex Ledeb., evaluate qualitative and quantitative criteria for the hybrid similarities and differences with its parental species, as well as to analyze data on its habitat characteristics. Samples were collected in 2014-2016 from waterbodies in European Russia (Tver and Yaroslavl oblasts). In the study on biomorphology of S. × longifolium we used live and fixed materials, as well as herbarium funds of IBIW, MXA and MW. To establish and specify taxonomic features of the hybrid under study, indicating to its similarity with a certain ancestral species, our data on the morphology and ecology of S. emersum Rehm. and S. gramineum Georgi. are used. During field studies, the type of a water object where the hybrid was detected, ecological characteristics of its habitat (type of soil, depth, water temperature and pH) are determined; the list of taxa which enter into the cenosis composition is compiled. The biomorphological investigation of S. × longifolium shows that by life form this hybrid, as well as its parental species, is a vegetative-mobile evidently-polycentric annual or biennial plant of vegetative origin with a racemose root system. The following should be attributed to the characteristic features justifying the hybrid origin of S. × longifolium: 1) a wider, slightly carinated lamina (as in S. emersum); 2) a branched inflorescence (as in S. gramineum); 3) the lower covering leaf of inflorescence, often exceeding the total length of the latter; 4) fruits with a straight (as in S. emersum) as well as bent (as in S. gramineum) style. Interestingly, some populations of S. × longifolium are rich in terate forms that can be explained by back crossing with one of the parental species or pleiotropic mutation(s). It is established that S. × longifolium is not widespread in European Russia, is a typically freshwater species, occurring in the littoral zone of mesotrophic and dystrophic waterbodies (usually in lakes of glacier origin). At present, its appearance in lake ecosystems is due to accelerated eutrophication caused by increasing human activities. Perhaps earlier this hybrid formation occurred in peripheral zones of the range of S. gramineum under cyclic climate changes. Observations suggest that S. × longifolium exceeds S. gramineum in ecological potentials. At the same time, habitat features of the latter have an effect on the hybrid distribution potential (limitation of habitat spectrum) which is hardly exceed S. emersum by its ecological and coenotic characteristics.

It is located in the Tyoshe-Seryozhinsky karst area of the Oka-Sura karst region or Seryozhe-Panskoy karst lake district. Its creation is justified by the need to protect the rare species of living organisms, diverse types of vegetation, unique landscapes and plant communities that are concentrated in this territory. Despite the fact that in 1934 on the shore of the Great Lake in the Staraya Pustyn village the biological station of the State University of Nizhny Novgorod was founded, local flora of the karst lakes which are linked into a single system by the channel of the River Seryozha, remains insufficiently studied. In 2014 and 2015 the authors conducted a study of the flora of the Pustynsky lake-river complex. The collection of material for study of the taxonomic composition of the flora of the reservoirs and the collection of herbarium material were carried out by the route method from a rowing boat and, in part, by traversing along the shore. Taxonomic, ecological (including the spectrum of life forms of plants) and ecobiomorphological analysis of the flora, including the analysis of the ratio of its latitudinal and longitude elements, was carried out in cameral conditions. The taxonomic analysis of flora showed 162 species of vascular plants from 61 genera and 42 families, 6 of these species-Najas minor All., N. major All., Trapa natans L., Potamogeton praelongus Wulf., P. trichoides Cham. et Schlecht. and Carex bohemica Schreb, being included in the List of Rare and Protected Species on the Territory of Nizhny Novgorod oblast. On the basis of the annotated list of plant species, taxonomic, geographic, ecological-coenotic and ecobiomorphological analysis of the flora of the water reservoirs was made. We confirmed that the flora of the lake-river complex is traditional for this territory. Poaceae, Cyperaceae, Potamogetonaceae, Polygonaceae and Asteraceae belong to the dominant families and Potamogeton L., Carex L., Juncus L. and Salix L. belong to the dominant genera of the Pustynsky lake-river system. The level of the hybrid component of the flora is extremely low, which is typical for the watershed lakes. We found that a 6.5 km stretch of the Seryozha River accounts for about 30% of species of the vascular plants belonging to the flora in the Volga River basin. The high species richness of the flora of this territory is due, primarily, to the specific features of the shoreline, forming a broad range of habitats and the relatively stable water level regime despite the strong fluctuation in the level of anthropogenic pressure. We found that boreal and plurizonal elements dominate zonally but Holarctic and Eurasian species-regionally. The predominance of species typical for the ecotone zones of lakes (hygrophytes, hydrophytes and mesophytes) is an integral feature of the ecological-coenotic diversity which is characteristic of the Volga River basin. According to the Raunkiaer classification of life forms, hemicryptophytes are the most numerous group and the hamephytes are the least numerous one. A biomorpho...

Sparganium longifolium was reported as a hybrid between S. emersum and S. gramineum based on its intermediate type or the common characteristics of its parent species. Its hybrid origin needs to be confirmed using molecular technology. We investigated the origin of S. longifolium based on 10 populations of S. emersum, S. gramineum and S. longifolium from five lakes in European Russia, using sequences of six nuclear loci and one chloroplast DNA fragment. Haplotype network, principal coordinate analysis and genetic clustering based on data of nuclear loci confirmed that S. longifolium is the hybrid between S. emersum and S. gramineum. We found that the natural hybridization between S. emersum and S. gramineum is bidirectional but asymmetrical, and the latter mainly acts as maternal species. We also found that all samples of S. longifolium were F1 generations, and thus hypothesized that S. emersum and S. gramineum could likely maintain their species boundary through the post-zygote reproductive isolation mechanism of F1 generation sterility.