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Last Updated: Spring 2012

Synonyms: NONE

Family: Trapaceae

Home Range/U.S. Introduction:
Trapa natans L. is native to Eurasia and is naturalized in North America. It is frequently cultivated in Asia and elsewhere where the fruit is eaten. Water chestnut was introduced into North America about 1874 and was cultivated in the botanical garden at Harvard University in the late 1870’s and later escaped to nearby ponds and lakes. It ranges from Massachusetts, to western Vermont, eastern New York, Maryland, and Virginia (Crow & Hellquist 1983).

U.S. Range Map:

Distribution was determined by a combining of the distribution information obtained from the following websites:

USDA, NRCS. 2012. The PLANTS Database (http://plants.usda.gov, 18 June 2012). National Plant Data Team, Greensboro, NC 27401-4901 USA.

U.S. Geological Survey. [2012]. Nonindigenous Aquatic Species Database. Gainesville, Florida. Accessed [6/18/2012].

Species Description:
Water chestnut is an annual with elongate, mostly simple stems which grows submersed, rooted in the substrate. Leaves are of two types: (1) submersed ones are alternate, sessile, linear and entire, falling off early in the growth of the stem, and (2) a rosette of floating leaves with inflated petioles to 15 cm long, the blades diamond-shaped (4-sided) or nearly triangular with toothed margins, the upper surface glossy and the lower surface pubescent. After the submersed leaves drop off, green, adventitious (occurring out of order) roots, up to 8 cm long, that are pinnately dissected into filiform segments develop in their place. These roots are often mistaken for leaves. The flowers are above the water surface, solitary on axillary peduncles. The petals are white, about 8 mm long. The fruit is a woody or bony nut, about 3 cm wide, with stout spines.

Habitat/Growth Characteristics:
Plants grow rooted in soft mud in lakes, ponds, canals and slow backwaters and bays of rivers, in up to 5 m of water. Mature nuts sink to the bottom and may germinate for 1 year. If they are air-dried they die. These edible nuts are dispersed by animals and by water.

Plants form large populations and may be very troublesome to navigation, fisheries and recreation.

Crow, G. E. and C. B. Hellquist. 1983. Aquatic Vascular Plants of New England: Part 6. Trapaceae, Haloragaceae, Hippuridaceae. Station Bulletin 524. New Hampshire Agricultural Experiment Station, University of New Hampshire, Durham, New Hampshire.