Alternanthera philoxeroides (Mart.) Griseb.
Synonym(s): alligator weed, pig weed

Alligatorweed 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. Alligatorweed roots in wet soils or shallow water and grows out into waterways. Alligatorweed 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. Alligatorweed is native to South America and was first introduced into the United States around 1900 in ballast water.

Identification, Biology, Control and Management Resources