What does "pondweed" mean?

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

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