hydrilla
Hydrilla verticillata (L. f.) Royle

Overview

Appearance

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.

Foliage

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.

Flowers

Only the female flowers of this dioecious plant have been found in the United States, which means no viable seed are produced.

Fruit

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.

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
• California Noxious Weeds
• 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 Exotic Pest Plant Council - 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 Noxious Weeds
• 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
• 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