Alternanthera philoxeroides (Mart.) Griseb.

U.S. Nativity: Exotic
Habit: Aquatic

Synonym(s): alligator weed, pig weed

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.
Opposite, elliptical leaves are thick but non-succulent and are up to 4 in. (10 cm) long.
Flowering occurs during the summer with white, clover-like heads in the axils of the leaves.
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.

Identification, Biology, Control and Management 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