Water Chestnut
Trapa natans

Water chestnut is an invasive aquatic plant with rosettes of triangular leaves that float on the water’s surface. It grows in the Bird and Sassafras rivers, which are tributaries of the upper Chesapeake Bay.

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A section of river filled with water chestnut and American lotus plants. There are flower buds but neither type of plant is in bloom. In the background, two humans wade through the plants.
Water chestnut floats between American lotus plants in the Sassafras River on the border between Cecil County and Kent County, Md., on July 14, 2010. (Photo by Alicia Pimental/Chesapeake Bay Program)

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Appearance

The water chestnut's triangular or diamond-shaped leaves form rosettes that float on the water’s surface. The leaves have teeth along the edges, a shiny upper side and fine hairs underneath. Thread-like leaves grow alternately along the submerged part of the stem.

Tiny, white flowers bloom in June to July. Hard, greenish-brown fruits with four sharp spikes are attached to the plant’s underside in spring and early summer. Water chestnut can float freely or be rooted to bottom sediments.

Reproduction and life cycle

Water chestnut can reproduce both sexually and asexually. Sexual reproduction takes place in early summer. After being fertilized, female flowers mature into fruit-bearing shoots. The shoots eventually break off, releasing their seeds as they float on the surface.

Asexual reproduction takes place when the rhizome (underwater portion of the plant's stem) grows and winter buds, called "turions," form.

Did you know?

  • It is believed that water chestnut was introduced in the mid-1800s for ornamental use in ponds.
  • Water chestnut is considered to be invasive because it blocks sunlight from reaching bay grasses and can impede boat navigation. The plant’s sharp, spiky fruits are dangerous to humans swimming or walking on beaches.

Sources and additional information

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