Choke pondweed

from The Collaborative International Dictionary of English v.0.48

Pondweed \Pond"weed`\, n. (Bot.)
   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.
      [1913 Webster]