Native Range

Africa, Asia, Australia, and Eastern Europe

Appearance

Hydrilla is a submersed, aquatic perennial with roots typically buried in the hydrosoil, though fragmented plants can also form free-floating mats at the water surface. Roots are slender; some are stoloniferous and terminate in small tubers while others are connected to another hydrilla plant. Stems are up to 30 ft (9 m) long and are often branched near the water surface, forming dense intertwined mats. Leaves occur in whorls of 3–8 all along the stem. Each leaf has serrated margins and small teeth on the underside of th midvein. Swollen, dormant leaf buds (turions) are formed in leaf axils. Flowers are tiny and may be closely attached to leaf axils or to thread-like stalks.

Impact

Hydrilla displaces native species, impedes water flow, and damages several recreational sectors including fishing, hunting, boating, and swimming. Decaying plant material can decrease oxygen levels which is detrimental to fish and other organisms. Dense infestations cause stagnant water conditions that create habitat for organisms that cause or transmit disease.

Reference

Harms, N.E., M. Purcell, and G.S. Wheeler. 2022. Hydrilla (Hydrilla verticillata): History and Ecology in North America. In: R.L. Winston, Ed. Biological Control of Weeds in North America. North American Invasive Species Management Association, Milwaukee, WI. NAISMA-BCW-2022-32-HYDRILLA-P. https://bugwoodcloud.org/resource/files/23222.pdf

Resources

• Fact Sheet - Ontarios Invading Species Awareness Program
• Biological Control of Invasive Plants in the Eastern United States - USDA Forest Service
• Southeast Exotic Pest Plant Council Invasive Plant Manual - SE-EPPC
• Element Stewardship Abstract - The Nature Conservancy
• Federal Noxious Weed Disseminules of the U.S. - USDA-APHIS
• Weed of the Week - USDA Forest Service
• Global Invasive Species Database - Invasive Species Specialist Group
• Plant Invaders of Mid-Atlantic Natural Areas - National Park Service and U.S. Fish and Wildlife Service

Selected Images

Maps

Invasive Listing Sources

• Alabama Invasive Plant Council
• Alachua County Cogongrass Initiative
• Alberta Fisheries Act
• Apalachicola Invasive Working Group
• Arizona Noxious Weeds
• California Invasive Plant Council
• Colorado Noxious Weeds
• Connecticut Invasive Plant List
• Connecticut Invasive Plant Working Group
• Delaware Invasive Species Council
• Delaware Invasive Species Council Invasive Species List
• Federal Noxious Weeds
• Florida Invasive Plant Council - Plant List - Category I
• Florida Noxious Weeds
• Georgia Exotic Pest Plant Council - Category 1
• Idaho Noxious Weeds
• Indiana Invasive Species Council - Invasive Plant List
• Indiana Pest Species
• Indiana Prohibited Plant Species
• Invasive Plant Species of West Virginia
• Invasive Species of Concern in Georgia
• 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.
• Kentucky Exotic Pest Plant Council - Significant Threat
• Maryland Aquatic Nuisance Species Plan
• Maryland Code and Regulations Nonative Aquatic Organisms
• Maryland Department of Natural Resources Policy: Restriction on Planting Exotic Invasive Plants
• Maryland Invasive Species Council - Invasive Species of Concern in Maryland
• Massachusetts Invasive Plants Advisory Group List
• Massachusetts Noxious Weeds
• Massachusetts Prohibited Plant List
• Michigan’s Invasive Species Watch List
• Michigan’s Prohibited and Restricted Species
• Mid-Atlantic Field Guide to Aquatic Invasive Species
• Minnesota DNR invasive species list
• Mississippi Noxious Weeds
• Montana Noxious Weeds
• National Park Service, Mid-Atlantic Exotic Plant Management Team Invasive Plant List
• Native Plant Society of Oregon, 2008
• Nevada EDRR
• Nevada Noxious Weeds
• 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.
• New Hampshire Prohibited Aquatic Species
• New Jersey Invasive Species Strike Team 2017 Invasive Species List
• New Mexico Noxious Weeds
• New York Regulated and Prohibited Invasive Species - Prohibited
• Non-Native Invasive Plants of Arlington County, Virginia
• Non-Native Invasive Plants of the City of Alexandria, Virginia
• Nonnative Invasive Species in Southern Forest and Grassland Ecosystems
• Ontario’s Invading Species Awareness Program Tracked Species List
• Oregon Noxious Weeds
• Pacific Northwest Exotic Pest Plant Council, 1998
• Pennsylvania Department of Conservation and Natural Resources Invasive Plants
• Pennsylvania Noxious Weeds
• Pennsylvania Regulations for Controlled Plants and Noxious Weeds
• Pennsylvania's Field Guide to Aquatic Invasive Species
• Plant Invaders of Mid-Atlantic Natural Areas
• South Carolina Illegal Aquatic Plants
• South Carolina Plant Pest List
• Tennessee Exotic Pest Plant Council
• Texas Noxious Weeds
• USDA APHIS Regulated Pest List
• Vermont Noxious Weeds
• Virginia Invasive Plant Species List
• Virginia Noxious Weeds
• Washington Noxious Weeds
• WeedUS - Database of Plants Invading Natural Areas in the United States
• West Virginia Invasive Species Strategic Plan and Volunteer Guidelines 2014
• West Virginia Native Plant Society, Flora West Virginia Project, and West Virginia Curatorial Database System, September 3, 1999
• Wisconsin Noxious Weeds
• Wisconsin's Invasive species rule – NR 40

References