Water Chestnut

Photo credit: © Fredy Wyss/Flickr

(Trapa natans)

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If you believe you have found this species anywhere in Pennsylvania, please report your findings to iMapInvasives by submitting an observation record.

Species at a Glance

Water chestnut is a rooted aquatic plant, very different from the one you find in Chinese take-out. It can dominate ponds, shallow lakes, and rivers because it grows in thick, dense colonies and can grow as much as 4.8 m (16 ft) in length.

Identification

Leaves: Come in two distinct forms: floating and submersed. Floating leaves are triangular or fan-shaped with noticeably toothed margins on the outer edges. They are roughly 1-3 cm (0.4-1.2 in) long and are arranged in large floating rosettes. The upper leaf surface is glossy, while the underside is covered with soft hairs. These leaves are kept afloat by spongy, inflated bladders attached to long stems called petioles (up to 15 cm [5.9 in]), which connect the leaves to the submersed section of the plant. The submersed leaves are green and feathery, and whorl around the cord-like stem.

 

Flowers: Small flowers, about 1 cm (0.4 in) long with four white petals located in the center of the leafy rosette, and usually appear in mid-to-late July.

 

Fruits/Seeds: Black nut-like structures have four spiny projections that are so sharp they are capable of penetrating shoe leather.

 

Stems/Roots: Numerous finely branched roots develop along the lower stem, which assist in anchoring the plant to the substrate.

Similar Species

None.

Habitat

Water chestnut can grow in any freshwater setting, but prefers nutrient rich waters less than 4.8 m (16 ft) deep in ponds, lakes, slow moving streams, and rivers.

Spread

Water chestnut has a high reproductive rate, with each plant producing up to 15 nuts per season. Each nut can sink to the bottom and remain viable for up to 12 years. It can also spread vegetatively when the rosettes of floating leaves break apart and fragments attach to boats and trailers or float to new locations.

Distribution

The native range of water chestnut includes Europe, Asia, and Africa. It was brought to the United States by water gardeners in the 1800s and quickly established, with the first known occurrence in Massachusetts. In the Mid-Atlantic, it has spread to the waters of Delaware, Maryland, New Jersey, New York, Pennsylvania, Virginia, Washington DC, and West Virginia.

 

Note: Distribution data for this species may have changed since the publication of the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016), the source of information for this description.

Environmental Impacts

The dense floating mats of water chestnut can choke a water body, limiting light and oxygen and impeding boating and other recreational activities. Colonies of this plant can outcompete native organisms for nutrients and space, while offering little nutritional value for wildlife.

Videos
Note

Information for this species profile comes from the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016).

The Pennsylvania iMapInvasives Program is a partnership of the Western Pennsylvania Conservancy, the Pennsylvania Natural Heritage Program, and NatureServe.

Funding for Pennsylvania iMapInvasives is provided by the Great Lakes Restoration Initiative.

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Pennsylvania Natural Heritage Program, iMapInvasives partner
Great Lakes Restoration Initiative logo, iMapInvasives funding source