Water chestnut (Trapas nantans L.) is an aquatic plant that bears a rosette of floating leaves at the top of the submerged and rooted stem.
Origin/Introduction:
Water chestnut is native to Eurasia. It was intentionally introduced at the Cambridge Botanical Garden, and in a pond in Concord, Massachusetts in the 1800s where it escaped cultivation and spread throughout the northeast U.S.
Habitat:
Water chestnut can be found in freshwater lakes and ponds and prefers slow-moving shallow waters high in nutrients with a neutral or alkaline pH.
This fast-growing, aquatic plant forms large mats that shade out native aquatic vegetation and has the ability to completely dominate surface waters. It reduces oxygen levels for fish and encourages sedimentation by restricting silt movement. Hard, pointy seeds can penetrate shoe leather if stepped on.
Leaves: Float on the surface forming a rosette and are waxy, triangular and toothed. Green, feather-like, submersed leaves on the underwater portion of the stem are paired and are considered by some to be modified roots.
Petioles: Have a bladder-like swelling filled with air and spongy tissue that provides buoyancy to the floating rosette.
Flowers: The inconspicuous flowers with their four white petals, each about 1/3 inch long, are borne singly on erect stalks located in the central area of the leafy rosette. Blooms occur in mid to late July and continue until frost.
Seeds: a black, four-horned, nut-like structure, about an inch wide, that develops underwater. Each seed can produce 10 – 15 new plants; in turn, each rosette can produce 15 – 20 seeds. Seeds are easily dispersed in water and can remain viable in sediment for 12 years.
Stem: stems are elongate, typically about a meter long but may reach as much as 5 meters in length.
Control/Management:
Note: Because water chestnut produces a large number of seeds, treatments may have to be repeated until the seed bank in the sediment is exhausted.
Physical/Mechanical Control: Depending on the size of the infestation, water chestnut populations can be managed by hand pulling rosettes (floating portion) after the seeds have formed but before they are ripe (early August). Mechanical harvesters can be used as well but may be costly. Take care to remove all plant fragments as plants can regenerate.
Chemical Control: Larger infestations of water chestnut can be controlled by herbicides; use of chemical application is effective in controlling annual growth of the plant but not the ripened seeds (which remain viable up to 12 years!), therefore, herbicides should be applied before seeds are produced (June).
Permits are required for herbicide use and must be applied by a licensed applicator.
Photo Credits:
Title photo: Erica Burgeson pulling water chestnut. Credit: Katie Little, The Nature Conservancy.
Leaves photos: top photo, http://www.thesurvivalchannel.com/post-4617-WaterChestnutWaterCaltrop.html.
bottom (illustrated)photo, http://www.goodyearlakeny.org/our-lake.html
Petioles photo: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org.
Flower photo: Ohsaka City University Botanical Garden, http://flowers.la.coocan.jp/Lythraceae/Trapa%20natans%20quadrispinosa.htm
Seeds photo: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org.
Stem photo: Roberta Hill, Maine Volunteer Lake Monitoring Program (VLMP) 2007, http://www.mainevlmp.org/mciap/herbarium/WaterChestnut.php
PREVENTION
Prevent the introduction of invasive species into the SLELO PRISM.
EARLY DETECTION & RAPID RESPONSE
Rapidly detect new and recent invaders and eliminate all individuals within a specific area.
COOPERATION
Share resources, including funding personnel, equipment, information, and expertise.
INFORMATION MANAGEMENT
Collect, utilize, and share information regarding surveys, infestations, control methods, monitoring, and research.
CONTROL
Control invasive species infestations by using best management practices, methods and techniques to include: ERADICATION (which is to eliminate all individuals and the seed bank from an area), CONTAINMENT (which is reducing the spread of established infestations from entering an uninfested area) and SUPPRESSION which is to reduce the density but not necessarily the total infested area.
RESTORATION
Develop and implement effective restoration methods for areas that have been degraded by invasive species and where suppression or control has taken place.
EDUCATION & OUTREACH
Increase public awareness and understanding of invasive species.
INNOVATION
Develop and implement innovative technologies that help us to better understand, visualize, alleviate or manage invasive species and their impacts or that serve to strengthen ecosystem function and/or processes.
Rob Williams
PRISM Coordinator
Megan Pistolese
Outreach and Education
Brittney Rogers
Aquatic Invasive Species
Robert Smith
Terrestrial Invasive Species