Noun
Any of several North American aquatic plants
Elodea canadensis, in the Hydrocharitaceae family, with many small leaves on a submerged stem
(UK) Potamogeton epihydrus, in the family Potamogetonaceae.
Potamogeton nodosus, in the family Potamogetonaceae, with large floating leaves borne on elongated petioles
Source: en.wiktionary.org