First report of Wolffia columbiana and W. globosa in France
Two species of Wolffia have been recorded from France in 2020, namely Wolffia columbiana and W. globosa (Araceae). W. columbiana was discovered in the north of France in the Hauts-de-France region, and W. globosa was discovered in the south of the territory in the Occitanie region. Wolffia columbiana is native to North America and W. globosa is native to Asia. In France there is also one native species in this genus; W. arrhiza. The genus Wolffia comprises of 11 species of minute floating aquatic plants and distinguishing the three species is not easy. W. globosa was first discovered in Bulgaria in 2010 and more recently in Germany in 2020 and W. columbiana was recorded in Germany and the Netherlands in 2013 and more recently in Italy and Belgium. In France, the non-native Wolffia species have contrasting suitability to resistance to cold temperatures. W. columbiana can withstand temperatures as low as -12oC whereas W. globosa can only tolerate temperatures down to 1oC. Migratory birds which pick up the plants on their feet and in their feathers can be vectors for spread, and it can also be spread as a contaminant of aquatic plants in trade. The latter is the probable pathway for entry into the EPPO region. In France, both non-native species show signs of invasive potential and may threaten the native W. arrhiza. The authors provide a key to distinguish the species present in Europe.
Sources
Lecron JM, Fisson P, Fried G, Lierout M, Niebler F, Verloove F (2021) Deux nouvelles espèces de wolffies en France mėtropolitaine: Wolffia columbiana H. Karst. et W. globosa (Roxb.) Hartog & Plas (Araceae). Bulletin de la Société botanique du Centre-Quest 52, 129-136.