pondweed, n.
Any aquatic plant of the genus Potamogeton, of which many species are found in ponds or slow-moving rivers. [1913 Webster]
Choke pondweed, an American water weed (Anarcharis Canadensis, syn. Elodea Canadensis.) See Anacharis. -- Horned pondweed, the Zannichellia palustris, a slender, branching aquatic plant, having pointed nutlets.