First report of Wolffia columbiana in Italy
Wolffia columbiana (Araceae) was discovered in a pond in the Lombardia region of Italy in March 2016. The species was identified to be distinct from the only native species of Wolffia, W. arrhiza, which occurs throughout Europe. W. columbiana is an aquatic floating perennial herb without any roots. The fronds are single or joined, and spherical to widely ellipsoid in shape: 0.77 – 0.9 mm long, 0.67 – 0.73 mm wide. The native range of Wolffia columbiana extends through the temperate and tropical regions of North and South America, from Canada southwards to Argentina. Outside the Americas, it is known only from Central and Western Europe, in over 80 localities in Germany and the Netherlands. The waterbody where W. columbiana was recorded in Italy consists of a small pond along the bank of the river Po. The likely pathway for the entry of W. columbiana into the EPPO region is as a contaminant of aquatic ornamental plants.
Ardenghi NMG, Armstrong WP, Paganelli D (2017) Wolffia columbiana (Araceae, Lemnoideae): first record of the smallest alien flowering plant in southern Europe and Italy. Botany Letters 164, 121-127.