SWAMP SMARTWEED, Polygonum coccineum Muhl. 1, upper part of plant; 2, portion of rhizome; 3, seed. Perennial, reproducing by long, creeping, tough, woody, horizontal rhizomes and by seed. Stems erect, 1 to 3 feet (0.3 to 0.9 m) long, enlarged at nodes, usually unbranched; may produce roots at nodes. Leaves alternate, oblong, 2-1/2 to 8 inches (6.3 to 20 cm) long, pointed at tip, rounded at base with prominent veins. A sheath at base of each leaf surrounds stem. Flowers rose in color and produced in compact erect spike I to 3 inches (2.5 to 7.5 cm) long. Seeds oval, flattened on one side, black, shiny, and slightly rough; however, not usually produced in northern areas. Found usually in low, wet places in fields, gardens, or roadsides, but may be present elsewhere. The extensive root system makes it a strong competitor with other plants and difficult to kill. Also commonly known as tanweed and devil's shoestring.