WATER CHESTNUT
(Trapa natans)
The
water chestnut is an annual aquatic plant that is found in slow moving,
nutrient-filled waters such as ponds, lakes, streams, and rivers.
ORIGIN
Europe, Asia, and Africa
HABITAT
Water chestnut grows in nutrient-rich shallow lakes and rivers throughout
the eastern United States.
IDENTIFICATION
It consists of a submerged stem that attaches to a buoyant rosette of
leaves. Flowers are small, white, and form at the center of the stems.
The stems can reach 4-5 m (12-15 ft) in length. The nut portion of the
water chestnut plant has four very strong, sharp spines that sprout from
the bottom sediment.
Water chestnuts begin to flower in mid to late July, with their nuts ripening approximately one month later. Flowering and seed production continue into the fall when frost kills the floating rosettes. Each nut that sinks to the bottom may produce new plants; nuts are viable for up to 12 years with a high percentage germinating in the first two years.
 Water Chestnut Flower |
 Nut portion of plant showing spines |
SPREAD
The introduction of the water chestnut to the eastern United States is
thought to have occurred during the 1870s. Most new introductions are
related to water gardening. The plant can also spread by the rosettes
detaching from their stems and floating to another area. In Pennsylvania,
the plant overwinters entirely by seed. After germinating, the water chestnut
plant develops at a rapid rate.
2010 Distribution of Water Chestnut
IMPACTS
This prolific plant can cover a water body with a dense mat of vegetation,
causing significant damage to the health of the aquatic ecosystem. Water
chestnut can also limit boating and fishing in infested areas. It has
the potential to infest wetlands and critical environmental habitats in
other areas of the state.
Other impacts include:
- The water chestnut seed is a danger to bathers and beachcombers; its hard spikes are capable of tearing through shoe leather
- Water chestnut colonization creates a canopy that interrupts the passage of light through water, which is necessary to maintain a well-functioning ecosystem.
- Water chestnut colonies crowd out and alter the habitat of many native species.
- The dense mats created by water chestnut outbreaks can block waterways for boaters.
PREVENTION
AND CONTROL
Mechanical control is the most effective way to treat water chestnut.
Eradication of water chestnut on the Sassafras River (tributary to the
Chesapeake Bay) was achieved by pulling plants before they developed seeds.
The complete removal of the entire plant is imperative because small pieces
of plant can spread the invader to a new location. Biological controls are being investigated, but no species have been approved
for release.
To read more, view the Pennsylvania Sea Grant Water Chestnut fact sheet.
FOR MORE INFORMATION ON WATER CHESTNUT
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