Alternanthera philoxeroides (Mart.) Griseb.

Alligator Weed

Herb

Perennial

Vascular

Alligator Weed is an introduced herbaceous perennial in the Amaranth family (Amaranthaceae). It is native to the temperate regions of South America. In Alabama in can be found throughout the state. Alligator Weed is a stoloniferous plant inhabiting aquatic and semi-aquatic areas. It can be found in lakes and ponds, in sloughs, on river banks, in roadside ditches, and in frequently flooded forests. Stems are prostrate, rooting at the nodes or forming floating mats. The stems are green in color and glabrous. Floating stems are hollow and stems on terrestrial plants are solid with spongy pith. Leaves are opposite, sessile, elliptic to oblanceolate in outline, entire, and glabrous. Flowers are produced in pedunculate terminal and axillary heads. Each flower has 5 papery white tepals. The fruit is an utricle. Plants in North America have not been observed to produce fruit or seed. Alligator Weed is listed as a Category 1 invasive plant species by the Alabama Invasive Plant Council. It reproduces rapidly from small segments of stem that root in water or mud. Alligator Weed forms dense mats along the shores of water bodies that impact swimming, fishing, and boating. It can clog waterways and exclude native species. The Alligator Weed Flea Beetle (Agasicles hygrophila) has been introduced in the United States as a biological control.—A. Diamond

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Not Native OBL (NWPL)

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