alligatorweed
(Alternanthera philoxeroides (Mart.) Griseb.)

Overview

Appearance

Alternanthera philoxeroides is an emergent or rooted floating plant that invades aquatic areas and adjoining uplands throughout the southern portions of the United States. Plants have hollow stems and can grow to 3 ft. (1 m) tall.

Foliage

Opposite, elliptical leaves are thick but non-succulent and are up to 4 in. (10 cm) long.

Flowers

Flowering occurs during the summer with white, clover-like heads in the axils of the leaves.

Fruit

Fruits are very small, and single-seeded.

Ecological Threat

Alternanthera philoxeroides roots in wet soils or shallow water and grows out into waterways. Alternanthera philoxeroides can also grow terrestrially, forming smaller, tougher leaves. The thick mats can displace native vegetation and wildlife habitat, clog waterways, restrict oxygen levels of water, increase sedimentation, interfere with irrigation and prevent drainage. It is native to South America and was first introduced into the United States around 1900 in ballast water.

Resources

• Biological Control of Invasive Plants in the Eastern United States - USDA Forest Service
• Invasive Alien Plant Species of Virginia - Virginia DCR and Virginia Native Plant Society
• Global Invasive Species Database - Invasive Species Specialist Group
• Images, Video and Information - University of Florida - Center for Aquatic and Invasive Plants

Selected Images

Maps

Invasive Listing Sources

• Alabama Invasive Plant Council
• Alabama Noxious Weeds - Class C Noxious Weed
• Alachua County Cogongrass Initiative
• Apalachicola Invasive Working Group - Low
• California Invasive Plant Council
• California Noxious Weeds
• Florida Invasive Plant Council - Plant List - Category II
• Florida Noxious Weeds
• Georgia Exotic Pest Plant Council - Category 1
• 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 Department of Natural Resources Policy: Restriction on Planting Exotic Invasive Plants
• Mid-Atlantic Field Guide to Aquatic Invasive Species
• National Park Service, Mid-Atlantic Exotic Plant Management Team Invasive Plant List
• National Park Service, National Capital Region Exotic Plant Management Team Invasive Plant List
• Non-Native Invasive Plants of Arlington County, Virginia
• Nonnative Invasive Species in Southern Forest and Grassland Ecosystems
• South Carolina Illegal Aquatic Plants
• South Carolina Plant Pest List
• Tennessee Exotic Pest Plant Council
• Texas Noxious Weeds
• To be proposed for MISC
• Virginia Invasive Plant Species List
• WeedUS - Database of Plants Invading Natural Areas in the United States
• West Virginia Native Plant Society, Flora West Virginia Project, and West Virginia Curatorial Database System, September 3, 1999

References