Invasive Aquatic Alert!–Two Horned Trapa

May 3, 2023
  |   1 Comment

Two Horned Trapa reporting–Please help us!

If you are around any ponds in Montgomery County, or anywhere else in Maryland, Virginia, or elsewhere, please report two-horned trapa!

Please help us to make two-horned trapa observations this season. This aquatic annual has infested 78 ponds in Northern Virginia. In 2022, recent infestations were found in Richmond, VA and Greenbelt, MD. It is not found elsewhere in North America. By working together to actively seek out trapa populations, we can prevent this plant from infesting the Chesapeake Bay where it would be devastating to shallow water habitats, and would hinder many forms of recreation and commerce.

Plants in the Trapa genus are easy to recognize because of their distinctive, four-sided leaves, two sides are toothed and two are straight. These leaves are arranged in a geometrically compact, floating rosette.

A floating rosette with the unique 4-sided leaves and pale pink flower.

Trapa is spread easily by birds, particularly geese and ducks, and can spread between ponds and slow moving rivers very fast.

Report it!

If you do find trapa, note the location, enter into iNaturalist if you use the app, and snap photos of a rosette (with a flower if possible), and seed pods if present. Step back and take a photo of the context! Include notes about the extent of the infestation, and the address.

If you do not have the INaturalist app, you can report it in Montgomery County to Department of Environmental Protection by emailing Check with parks or environmental agencies in other jurisdictions on how to report, and help us stop the spread!

Want more information? Check out this blog

A spent seed pod (spines are worn down).


A monoculture in a Northern Virginia farm pond.


One comment on "Invasive Aquatic Alert!–Two Horned Trapa"

  1. elastic man says:

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