Alligatorweed

Alternanthera philoxeroides

Weed Description
Aquatic mat-forming perennial that usually spreads vegetatively by fragmentation. Alligatorweed is an invasive aquatic weed that can be found in the coastal plain from Virginia to Florida and westward to Texas. This weed is now also found in coastal California.

Leaves
Opposite, elliptic in outline, from 2 to 4 inches in length. Leaves have a distinctive midrib, are without hairs (glaucous), and are without petioles.

Stems
Fleshy and succulent, light to dark green or pink to purplish in color, and reach 3 feet in length. Stems root at the nodes and are usually floating or trailing along the ground except for the tips that turn upward (decumbent). Stems are generally without hairs (glabrous) except for a few that occur at the leaf base.

Flowers
Relatively small (13 mm in diameter) and white in color. Flowers occur on flower stalks (peduncle) that are approximately 1/2 to 3 inches in length. Flowering usually occurs from April through October.

Roots
Fibrous roots occur at the stem nodes. Roots can be free-floating in water or occur in the soil.

Identifying Characteristics
Aquatic mat forming perennial with hollow stems, opposite leaves, and solitary white flowers.

Office of Programs

University of Missouri

Alligatorweed

Alternanthera philoxeroides