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Horned Pondweed

Zannichellia palustris

Horned pondweed has long, thread-like leaves along slender, branching stems. (Maryland Department of Natural Resources)
Horned pondweed has long, thread-like leaves along slender, branching stems. (Maryland Department of Natural Resources)

Horned pondweed is a bay grass with long, thread-like leaves and distinctive horned seeds in spring. It grows in fresh and medium-salinity tidal waters of the Chesapeake Bay and its rivers.

Appearance:

  • Long, thread-like leaves that taper to a point at the tips
  • Leaves can be up to 3 inches long
  • Leaves grow opposite or in whorls along slender, branching stems
  • In spring, slightly curved seeds with tiny horns grow in groups of 2-4 at the leaf axil
  • Thin rhizomes and short, tendril-like roots
  • Grows in two forms: an upright form with free-floating branches, and a creeping form with roots that anchor the plant to the bottom. The second form is common in winter and in areas with lots of waves.

Habitat:

  • Grows in low- to medium-salinity tidal waters
  • Generally found in shallow waters, but can grow to depths of 16 feet
  • Able to grow in both muddy and sandy sediments
  • Dies back in early summer when water temperatures warm

Range:

  • Found throughout the upper and middle Chesapeake Bay and its rivers

Predators:

  • Migratory waterfowl feed on the plant and its seeds

Reproduction and Life Cycle:

  • Only reproduces sexually
  • Seeds form in the spring and are released into the water by June
  • After releasing their seeds, the plants die back
  • Seeds generally germinate during the same year
  • This cycle may repeat itself in autumn if horned pondweed grows back after water temperatures cool

Other Facts:

  • Usually the first bay grass species to appear each spring
  • Can be confused with sago pondweed, slender pondweed and widgeon grass. Horned pondweed can be distinguished by its distinctive horned seeds and its leaves, which grow opposite or in whorls along the stems.

Sources and Additional Information:

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