hydrilla USDA PLANTS Symbol: HYVE3
U.S. Nativity: Exotic
Habit: Aquatic Plants Forbs/Herbs
Hydrilla verticillata (L. f.) Royle

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Taxonomic Rank: Liliopsida: Hydrocharitales: Hydrocharitaceae
Synonym(s): Florida elodea, water thyme, waterthyme
Native Range: Europe; Old World (BAIL);

Hydrilla verticillata is a submersed, rooted aquatic plant that can grow in water up to depths of 20 ft. (6.1 m). Plants can survive in depths up to 40 ft. (12 m) in non-turbid water.
Leaves are whorled in bunches of 3-8, but most often with whorls of 5. The midribs of the leaves are reddish in color with the undersides having small, raised teeth. Leaves are 0.2-0.8 in. (5-20 mm) long, less than 0.1 in. (2 mm) wide and have serrated margins.
Only the female flowers of this dioecious plant have been found in the United States, which means no viable seed are produced.
Turions (stem tubers) are bud-like structures which can drop off the plant and successfully survive freezing or drought. Tubers from the rhizomes are another way these plants reproduce and increase their invasive potential.
Ecological Threat
Hydrilla verticillata forms dense mats at the surface of the water. The dense mats can restrict native vegetation, irrigation practices, recreation, hydroelectric production, and water flow. It can invade most slow-moving or still water systems. This plant is believed to be native to Asia or Africa, although it is widely spread across the globe. It was first introduced into North America as an aquarium plant in the 1950s.

Identification, Biology, Control and Management Resources

Selected Images from Invasive.orgView All Images at Invasive.org

USDA APHIS PPQ - Oxford, North Carolina , USDA APHIS PPQ, Bugwood.org
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Plant(s); Discovered in the Crystal River in south Florida in 1960.
Raghavan Charudattan, University of Florida, Bugwood.org
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Robert Vidéki, Doronicum Kft., Bugwood.org
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Robert Vidéki, Doronicum Kft., Bugwood.org
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Robert Vidéki, Doronicum Kft., Bugwood.org
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Leslie J. Mehrhoff, University of Connecticut, Bugwood.org
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David J. Moorhead, University of Georgia, Bugwood.org
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Steve Hurst, USDA NRCS PLANTS Database, Bugwood.org
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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

State(s) Where Reported invasive.
Based on state level agency and organization lists of invasive plants from WeedUS database.

U.S. National Parks where reported invasive:
Colonial National Historical Park (Virginia)
George Washington Memorial Parkway (Virginia)
National Capital Parks East (Washington, D.C.)

Invasive Listing Sources:
Alabama Invasive Plant Council
California Invasive Plant Council
Connecticut Invasive Plant Working Group
Delaware Natural Resources and Environmental Control, 2004
Faith Campbell, 1998
Florida Exotic Pest Plant Council
Georgia Exotic Pest Plant Council
Gulf of Mexico Regional Panel, Aquatic Nuisance Species Annual Report, 2001
Jackie Poole, Texas Parks and Wildlife Department (personal communication)
Jil M. Swearingen, Survey of invasive plants occurring on National Park Service lands, 2000-2007
John Randall, The Nature Conservancy, Survey of TNC Preserves, 1995.
Maryland Department of Natural Resources, 1994
Mid-Atlantic Exotic Pest Plant Council, 2005
Native Plant Society of Oregon, 2008
New Hampshire Invasive Species Committee. 2005. Guide to Invasive Upland Plant Species in New Hampshire. New Hampshire Department of Agriculture,  Markets and Food Plant Industry Division and New Hampshire Invasive Species Committee.
North Carolina Division of Parks and Recreation, Department of Environment and Natural Resources, 1998
Pacific Northwest Exotic Pest Plant Council, 1998
Tennessee Exotic Pest Plant Council
Vermont Department of Environmental Conservation
Virginia Invasive Plant Species List