European water chestnut: Trapa natans (Myrtales: Trapaceae): Invasive Plant Atlas of the United States

European water chestnut	USDA PLANTS Symbol: TRNA U.S. Nativity: Exotic Habit: Aquatic Plants
Trapa natans L.

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Taxonomic Rank: Magnoliopsida: Myrtales: Trapaceae
Synonym(s): water chestnut, water nut
Native Range: Eurasia, Africa ()
Appearance Trapa natans is a rooted, floating plant that invades shallow to deep, fresh water habitats in the northeastern United States. It can grow in 12-15 ft. (3.6-4.6 m) of water and forms dense, floating mats, often three layers deep. Foliage The rosette of leaves on the surface of the water are alternate, triangular in shape, strongly dentate (toothed) and connected to the stem by an inflated petiole. Submerged leaves are feathery and either opposite or alternate. Flowers Trapa natans has small, four-petaled flowers that bloom from July to frost. Fruit The nut-like fruit has two to four, 0.5 in. (1.3 cm) long, sharp, barbed spines. They ripen in about a month and can remain viable as long as 12 years. Each seed can produce 1-15 rosettes and each rosette can produce as many as 20 seeds. The spines can penetrate shoes. Ecological Threat The dense, floating mats of Trapa natans restrict light availability, reduce the oxygen content, and displace other emergent and floating vegetation. It also limits boating, fishing, swimming and other recreational activities. Trapa natans is native to Europe and Asia and was first observed in the United States in Massachusetts in the late 1800s.

Identification, Biology, Control and Management Resources

Biological Control of Invasive Plants in the Eastern United States - USDA Forest Service
Global Invasive Species Database - Invasive Species Specialist Group
Plant Invaders of Mid-Atlantic Natural Areas - National Park Service and U.S. Fish and Wildlife Service
Fact Sheet - Ontarios Invading Species Awareness Program

Selected Images from Invasive.org

View All Images at Invasive.org

Feature(s); single rosette showing horned fruits and the inflated leaf petioles which enables the rosette to float Alfred Cofrancesco, U.S. Army Corps of Engineers, Bugwood.org Additional Resolutions & Image Usage	Flower(s); Leslie J. Mehrhoff, University of Connecticut, Bugwood.org Additional Resolutions & Image Usage	Plant(s); Floating rosettes Leslie J. Mehrhoff, University of Connecticut, Bugwood.org Additional Resolutions & Image Usage	Plant(s); Leslie J. Mehrhoff, University of Connecticut, Bugwood.org Additional Resolutions & Image Usage
Fruit(s); Leslie J. Mehrhoff, University of Connecticut, Bugwood.org Additional Resolutions & Image Usage	Fruit(s); Leslie J. Mehrhoff, University of Connecticut, Bugwood.org Additional Resolutions & Image Usage	Plant(s); Britton, N.L., and A. Brown. 1913. Illustrated flora of the northern states and Canada. Vol. 2: 612. USDA NRCS PLANTS Database , USDA NRCS PLANTS Database, Bugwood.org Additional Resolutions & Image Usage	Fruit(s); Steve Hurst, USDA NRCS PLANTS Database, Bugwood.org Additional Resolutions & Image Usage

EDDMapS Distribution:
This map is incomplete and is based only on current site and county level reports made by experts and records obtained from USDA Plants Database. For more information, visit www.eddmaps.org