(most commonly) Potamogeton, a diverse and worldwide genus / Elodea, found in North America / Aponogeton, in Africa, Asia and Australasia

plural of pondweed

Potamogeton epihydrus, a perennial aquatic plant.

Elodea canadensis, in the Hydrocharitaceae family, with many small leaves on a submerged stem / (UK) Potamogeton epihydrus, in the family Potamogetonaceae.