Horned Pondweed

Zannichellia palustris

Horned pondweed has slender, branching stems with:

• Long, thread-like leaves that taper to a point at the tips.
• Leaves can be up to 3 inches long and grow opposite or in whorls on the stems.
• Thin rhizomes and short, tendril-like roots.

Two forms of horned pondweed are found in the Bay:

• An upright form with branches that float freely.
• A creeping form with roots that anchor the plant to the bottom. This form is common in winter and in areas with high wave activity.

Where does horned pondweed grow?

Horned pondweed grows in fresh to moderately brackish waters in the Bay and its tributaries. It is generally found in shallow waters with a sandy or muddy bottom.

How does horned pondweed grow?

Horned pondweed only reproduces sexually.

• Horn-like, slightly curved seeds form in the spring.
• Seeds are released into the water by June, when the plants die back.
• The plant's fruit -- a dark, crescent-shaped nutlet -- forms rapidly.
• This cycle may repeat itself in the fall when horned pondweed grows back after water temperatures cool.

Other facts about horned pondweed:

• Horned pondweed can be confused with sago pondweed and widgeon grass. You can distinguish horned pondweed by its leaves, which grow opposite each other along the stems, and by its horned seeds.
• Both the plant and the seeds of horned pondweed are an important food source for waterfowl.
• Horned pondweed is usually the first underwater grass species to appear each spring; however, it declines in mid-summer because it cannot tolerate high water temperatures.