Horned Pondweed
Zannichellia palustris

Horned pondweed is an underwater 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.

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Seeds resembling horns grows off greenish-brown grassy stems.
Horned pondweed thrives in low- to medium-salinity tidal waters. (Photo by Alicia Pimental/Chesapeake Bay Program)

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Appearance

Horned pondweed is made up of long, thread-like leaves that taper to a point at the tips. Leaves can be up to 3 inches long. They grow opposite or in whorls along slender, branching stems. In spring, slightly curved seeds with tiny horns grow in groups of 2 to 4 at the leaf axil.

Horned pondweed has thin rhizomes and short, tendril-like roots. It grows in two forms: an upright form with free-floating branches, or 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.

Predators

Migratory waterfowl feed on the plant and its seeds.

Reproduction and life cycle

Horned pondweed 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.

Did you know?

  • Horned pondweed is usually the first underwater grass species to appear each spring.
  • Migratory waterfowl feed on the plant and its seeds.
  • It 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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