The situation of Pistia stratiotes in the EPPO region
In Russia, Pistia stratiotes (Araceae, EPPO Alert List) and Eichhornia crassipes (Pontederiaceae, EPPO A2 List) were recorded in 2003 in ponds and rivers of Moscow and its neighbourhood. Both species are grown for ornamental purposes and escape summertime cultivation, E. crassipes being also used for wastewater treatment. Despite forming large floating mats during hot summers, the first frosts of October kill these plants completely. The only area were they could be potentially invasive is Southern Russia. However, an overwintering population has been observed in 1993 in the Kazachii channel in the Volga delta in Astrakhan; it was able to thrive because of warm water discharged from a power station.
In Germany, P. stratiotes had been observed in the river Erft in 1981 as a consequence of warm water discharged from mining activities, but in 2005, the species was no longer found.
In Northern Spain, the botanist Aispuru collected the plant in 2001 in Guipuzcoa (Pais Vasco) as well as in Southern France, in the Landes deparment (lake of Garros, near the cities of Tarnos and Ondres). It was suggested that the species had been introduced by waterfowl. The species could not be found again in 2004 in the Landes, suggesting that the species was not able to establish. No recent information is available concerning the Spanish record in Pais Vasco. In Southern Spain, Pistia stratiotes was observed in 2005 in the Doñana National Park, forming monospecific stands 3 km long in a canal coming from the Guadalquivir river and receiving water from agricultural land. These waters were rich in nutrients, with traces of pesticides, and had a low oxygen content according to the analysis made by the Consejería de Medio Ambiante de Andalucía. These conditions did not allow growth of native hydrophyte species, but fitted P. stratiotes’ requirements. However, P. stratiotes is no longer found there.
In Slovenia, the species was also recorded as naturalized in a natural thermal stream (Topla) near čatez, where the water is at 17°C all year round. Plants developed and flowered from April to August. Over the winter, older rosettes decayed, but small rosettes survived, and new rosettes formed new stolons in spring. Viable seeds were also present in the sediments, although no seedlings were found. Only 2 years after its first occurrence in 2001, P. stratiotes had spread along 3 km and covered about 25 ha, and a decline in native vegetation was observed.
García Murillo P, Dana Sánchez ED, Rodríguez Hiraldo C (2005) Pistia stratiotes L. (Araceae) una planta acuática exotica en las proximidades del parque nacional de Doñana (SW España). Acta Botanica Malacitana 20, 235-236.
Šajna N, Haler M, Škornik S, Kaligarič M (2007) Survival and expansion of Pistia stratiotes L. in a thermal stream in Slovenia. Aquatic Botany 87, 75-79.
Schanzer IA, Shvetsov AN, Ivanov MV (2003) Eichhornia crassipes and Pistia stratiotes are spreading in ponds and rivers of Moscow and Moscow region. Byulleten Moskovskogo Obshchestva Ispytatelei Prirody Otdel Biologicheskii 108, 85-88.
Vivant J (2004) Plantes signalées dans les Landes et Pyrénées atlantiques en 2004. Blog de Jean Vivant. http://www.jean-vivant.net/doc_02.php