Source : Webster's Revised Unabridged Dictionary (1913)

Pondweed \Pond"weed`\, n. (Bot.)
   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.

Source : WordNet®

Zannichellia palustris
     n : found in still or slow-moving fresh or brackish water;
         useful to oxygenate cool water ponds and aquaria [syn: {horned
         pondweed}]