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.