Efremov, A.; Bolotova, Ya.; Mesterházy, A., and Toma, C., 2018. Features of distribution of Hydrilla verticillata (L. fil.) Royle (Hydrocharitaceae) in North Eurasia.

An assessment of Hydrilla verticillata (Hydrocharitaceae) distribution was made, with the involvement of a wide range of data (herbarium collections, Web resources, literature sources, and authors' observations), covering the period 1811–2016. It is shown that Hydrilla is a plurizonal macrothermal semicosmopolite species with many disjunctions in the geographical range. In the 20th century, H. verticillata expanded its secondary range significantly, primarily in North and South America (neocosmopolite). Within the primary range, in connection with high economic activities and development of transport, new invasion localities have appeared. For the European continent, H. verticillata should be considered a limitedly spreading naturalized neophyte (with the northern border at 55–56° N). In Northern Asia, H. verticillata can probably be considered a tertiary (Eocene) relict, which is currently allocated to the following enclaves: Central Asia–West Siberian, East Siberian (probably formed later), and the largest SE Asian habitats. The northern border of Hydrilla in the Asian continent lies along 56–58° N. Within the Asian part of the range the formation of new foci of infestation is currently observed, the species distribution is not controlled only by abiotic factors (temperature, length of vegetation period, hydrochemical features of the waterbodies), but also by biotic ones; there is a competition with the more aggressive neophyte Elodea canadensis.