Zannichellia palustris, the horned pondweed, is a plant found in fresh to brackish waters in the United States (especially in the Chesapeake Bay), Europe, Asia, Australasia, and South America. It is recognizable by its long, thread-like leaves and "stringy" appearance. Its roots are long and tendril-like, and its seeds bear a distinctive horned shape, hence the common name. The species epithet palustris is Latin for "of the marsh" and indicates its common habitat.Archibald William Smith A diploid, its chromosome number was confirmed as 2n = 24.Norio Tanaka, Yu Ito, Ruriko Matsuyama and Koichi Uehara (2007) Chromosome numbers of Zannichellia L. (Zannichelliaceae) in Japan. Bulletin of the National Museum of Nature and Science. Series B 33: 133-136
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