Alien aquatic plant species in European Russia.
The intense hydrobotanical investigations and high activity of international ornamental trade contributed to the list of the alien aquatic plant species in European Russia during several last decades (late 20th - early 21st centuries). However, the records from the Herbaria were not included in these reports. Our study aimed to complete this inventory by using multiple herbarium sources, our own field observations, and all publicly available references. In this region we identified 26 species of alien aquatic plants species by reporting multiple new localities and status of their invasiveness. Two species from Eastern Asia (Wolffia globosa, Monochoria korsakowii) have not been observed previously in Western, Central or Southern Europe. Ten species (53%) were originated from North and Central America, four species (21%) - from South America, three species (16%) - from tropics and subtropics of the Old World, one species (5%) - from the Far East, and one species (5%) - from Southeast Asia. We found that the aliens grow predominantly in the rivers with thermal inputs and artificial water bodies. Invasive species occasionally can be found in the non-disturbed aquatic communities, although most of these species have been established in the surroundings of the cities with dense population where they were introduced from aquarium and ornamental culture. According to the classification of invasive plants (Pyšek et al., 2004), twelve species (46%) are the outside cultivation casual plants, and eleven species (42%) are the alien outside cultivation naturalized non-invasive plants. Elodea canadensis Michx. and Lemna minuta Kunth are characterized by high invasiveness. Elodea nuttallii (Planch.) H. St. John most recently also showed more signs of being invasive.