water chestnut (Invasive Plants of Maryland)

water chestnut

Trapa natans

Description and biology ⁵

Plant: annual aquatic plant with a submerged stem; stems can reach 12-15 ft. in length; very fine roots anchor the plant into the mud.
Leaves: rosette of floating leaves at the water’s surface; saw-tooth margins; triangular in shape and connect to an inflated petiole which provides added buoyancy for the leafy portion; additional, feather-like leaves can be found along the submerged stem.
Flowers, fruits and seeds: flowers are four-petaled and white; form in June; are insect-pollinated; fruit is a nut with four ½-inch, barbed spines; seeds can remain viable for up to 12 years, although most will germinate within the first two years.
Spreads: by the rosette and by fruits detaching from the stem and floating to another area on currents or by clinging to birds and other floating objects.

Ecological threat in the united states ⁶

Water chestnut can form dense floating mats, severely limiting light – a critical element of aquatic ecosystems. Once established, it can reduce oxygen levels, increasing the potential for fish kills. It competes with native vegetation and is of little value to waterfowl. Water chestnut infestations limit boating, fishing, swimming and other recreational activities. Further, its sharp fruits, if stepped on, can cause painful wounds.

Distribution and habitat in the united states ⁷

Water chestnut can grow in any freshwater setting, from intertidal waters to 12 feet deep, although it prefers nutrient-rich lakes and rivers. Presently, the plant is found in Maryland, Massachusetts, New York and Pennsylvania, with most problematic populations occurring in the Connecticut River valley, Lake Champlain region, Hudson River, Potomac River and the upper Delaware River.

Prevention and control ⁸

Specialized methods of control are required to handle water chestnut infestations. Because of the likelihood of unintentional spread offsite and injury to those attempting control, only trained and certified persons should undertake management. Manual, mechanical and chemical techniques are used in its control. Complete removal of plants is imperative, as floating, uplifted plants and plant parts can spread the plant to new locations. It is critical that any removal take place prior to the July seed set. Eradication is difficult because water chestnut seeds may lay dormant for up to 12 years. Biological controls are being investigated, but no species have been approved for release.

Taxon biology ⁹

Water Chestnut (Trapa natans) is an annual, floating-leaved aquatic plant of temperate and tropical freshwater wetlands, rivers, lakes, ponds, and slightly brackish estuaries. It is native to Eurasia and Africa, where it has been widely gathered for its large nutritious seeds since the Neolithic. It is now widely distributed in Eurasia, Africa, and the northeastern United States.

Water Chestnut is viewed by humans quite differently in different parts of the world. It is cultivated for food in Asia. In Europe and Russia, it is now a species of conservation concern. However, in the northeastern United States, where it was introduced in the mid-1800s, it has spread widely and is viewed as a nuisance weed. Water Chestnut is considered a pest in the U.S. because it forms extensive, dense beds in lakes, rivers, and freshwater-tidal habitats. This results in displacement of aquatic plants; interference with boating, fishing, and swimming; and depletion of dissolved oxygen, which adversely affects fish communities. A range of control methods have been explored, including treatment with ultrasound (Wu and Wu 2006).

Two varieties of Water Chestnut are now generally recognized. The widespread variety of Water Chestnut, which produces a 4-horned fruit, is often known as Water Caltrop (T. natans var. natans) and is now found in Eurasia, Africa, and the northeastern United States. The other variety, often known as Singhara Nut (T. natans var. bispinosa) grows in China, Japan, India, and Southeast Asia and produces a fruit with two stout curved horns (according to Hummel and Kiviat [2004], this variety has at times been referred to as T. bicornis, T. bicornuta, and T. japonica). Although formerly placed in the family Trapaceae, modern treatments generally place Trapa in the Lythraceae (Graham et al. 2005). Water Chestnut should not be confused with the unrelated Chinese Water Chestnut (Eleocharis dulcis) (family Cyperaceae), a spikesedge with an edible tuber that is commonly used in Chinese cuisine.

Water Chestnut has floating leathery leaves, up to 5 cm wide, that are broadly triangular or ovate in outline with a toothed margin. The petiole (stalk) of each floating leaf has a spongy, swollen float that allows the foliage to form a rosette, up to 30 cm in diameter, on the surface of the water. Beneath the surface of the water is a flexible stem, 1 to 5 m long, that bears submersed, linear or spatulate leaves These submersed leaves drop early and are replaced by pairs of fine, pinnate structures up to 8 cm long. These plume-like structures have been variously considered to be stipules, leaves, or adventitious roots (i.e., roots originating from the stem, branches, leaves, or old woody roots rather than from primary roots). The small white 4-petaled flowers, which are borne singly in the axils of the floating leaves, yield dark brown woody fruits, 2.5 to 5 cm across, the outer portions of which quickly disintegrate to reveal the "nuts", which sink rapidly to the bottom where they overwinter in sediment.

Water Chestnut kernels contain 16% starch and 2% protein; because of possible toxicity, it is recommended to boil the kernels for an hour before consumption (Vaughan and Geissler 1997).

(Vaughan and Geissler 1997; Hummel and Kiviat 2004 and references therein) .

Sources and Credits

Jan Ševčík, no known copyright restrictions (public domain), https://www.biolib.cz/IMG/GAL/91050.jpg
(c) Karelj, some rights reserved (CC BY-SA), http://commons.wikimedia.org/wiki/File:Trapa_natans_Prague_2012_1.jpg
(c) Bart Wursten, some rights reserved (CC BY-NC), https://www.zimbabweflora.co.zw/speciesdata/images/14/142830-1.jpg
(c) Marco Schmidt, some rights reserved (CC BY-NC-SA), http://www.westafricanplants.senckenberg.de/root/index.php?page_id=14&id=1589
(c) Unknown, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/22733776
(c) Unknown, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/22733775
(c) Unknown, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/22733774
(c) Unknown, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/22733777
(c) Leo Shapiro, some rights reserved (CC BY), http://eol.org/data_objects/22951566

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water chestnut

Description and biology 5

Ecological threat in the united states 6

Distribution and habitat in the united states 7

Prevention and control 8

Taxon biology 9