Alligatorweed (Alternanthera philoxeroides)

Amaranthaceae (Pigweed family) 

Group: Dicot (broadleaf) 

Aquatic or terrestrial mat-forming perennial plant with underground runners, native of South America. The mats are dense, tangled stems, up to 3 feet long, and float in aquatic habitats or trail in terrestrial habitats. It is found in ditches and canals and in cultivated fields.  

Stem is red or pink, can be bigger than a thumb, round, often hollow, simple or branched, 1 to 3 feet long. Stems root at nodes. Nodes have hairs and are often swollen.  

Leaves are opposite, linear-elliptic or widest in the middle, with smooth and continuous margins. Leaves are sparsely hairy when young, without petioles or leaf stalks, and have a distinct midrib.  

Flower is a solitary head, round, and white on a long stalk.