Alligator weed

Emergent Plants

Alternanthera philoxeroides:

Alligator weed

Alternanthera philoxeroides (Mart.) Griseb.: Alligator weed. Amaranthaceae (pigweed family)

Exotic perennial. Rooted in submersed substrates, at shoreline, or in moist to dry soil. Herbaceous; forms dense stands of slightly fleshy growth. Stems are pinkish, usually hollow, upright to trailing, to 3.3 ft (1 m) long; on floating portions of the plant they can be swollen or inflated. Leaves are opposite, 2 - 5 in (5 - 12.5 cm) long, linear, oval, pointed to rounded at the top, and tipped with very small spines; they have distinct pale midveins and mostly smooth margins. Where the two narrowed leaf-bases join around the stem there is a small tuft of hairs. The stems form thickened joints at the leaf nodes; these readily produce roots, contributing to the plant's ability to spread. Flowers are interspersed with stiff bracts in white, round, clover-like heads borne singly on stalks in leaf axils. This plant can hinder access to waterways, and slow water movement.