Authors: Karan Rawlins, Hillery Reeves and Kaylee Tillery at the Center for Invasive Species & Ecosystem Health, University of Georgia
- 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.
- 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.
- Trapa natans has small, four-petaled flowers that bloom from July to frost.
- 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.
Global Invasive Species Database. 2011. Invasive Species Specialist Group (ISSG) of the IUCN Species Survival Commission 
University of Florida, IFAS Extension, Center for Aquatic and Invasive Plants 
Oregon Department of Agriculture Plant Programs, Noxious Weed Control 
Invasive Plant Atlas of New England (IPANE) 
Flora of China, www.eFloras.org 
USDA NRCS PLANTS 
USDA ARS GRIN 
Images from Bugwood.org