DESCRIPTION: Usually rooted in the mud, this aquatic plant has a rosette of floating leaves, 1/2 to 1 inch long, at the tip of a submersed stem, which can reach over 15 feet in length. The flowers of this species have four white petals about 1/3 of an inch long. The fruit is a black, four-horned nut-like structure that is about an inch wide and weighs approximately 6 grams. Water chestnut prefers shallow, nutrient-rich lakes and rivers.
LIFE CYCLE BIOLOGY: Within the United States, this species is an annual that can reproduce both by vegetative means and seed production. Each flower is bisexual and once the insect-pollinated flowers are fertilized the flower stalks curve downward with the result being the fruit develops underwater. Fruit fall to the floor of the water body over winter and seeds germinate in the spring. One acre of water chestnut can produce enough seeds to cover 100 acres the following year. Each seed can give rise to 10-15 rosettes and each rosette can produce as many as 20 seeds. Seeds can remain viable for up to 12 years.
DISPERSAL/SPREAD: The fruit of water chestnut may be dispersed when individual plants are uprooted and float downstream. These plants can also be dispersed by fragmentation. Due to the large size and weight of the sinking seeds, it is unlikely that waterfowl or water currents can transport seeds to any great extent.
RISKS/IMPACTS: Because of their ability to reproduce rapidly forming extensive floating mats, this species has become a nuisance in the United States, hindering navigation of waters and inhibiting the growth of native aquatic plant species. The hard spines on the fruit can impact swimming. Decomposition of this abundant plant species can also lead to lower oxygen levels in the water.
MANAGEMENT/PREVENTION: To help control the spread of this species, the sale of all species of Trapa has been banned in most of the southern United States. Mechanical control or repetitive harvesting of this species can is often employed, however this will not prove to be effective in the long-term due to the rapid reproductive rate of this plant. Attempts to control water chestnut with the aid of biological insects have been tried with no success.
The best means of control is prevention! Like all invasive species, the key to preventing their spread is knowledge! You can help by practicing a few good techniques to stop the spread of any aquatic invasive plant.
1) Learn to correctly identify water chestnut and other invasive aquatic plants.
2) Rinse any mud and/or debris from equipment and wading gear and drain any water from boats before leaving drainage areas.
3) Remove plant fragments from all equipment. The transportation of plant fragments on boats, trailers and in live wells is the main route of introduction to new lakes and rivers.
The spiked seed is of little value as food for wildfowl, although it may be a source of food for small aquatic animals. It can provide shade and cover for fish, however, it is a very aggressive plant and can shade and compete with more desirable species. The plant impacts boating and fishing additionally, the spiked seeds can wash up on beaches having a substantial negative impact on recreational use.