Native to Europe but introduced to North America, and found in nearly every state, in Mexico south into South America, and north throughout Canada to Alaska.
An emerged aquatic to semi-aquatic perennial or biennial. Reproduction is from seeds, and plants also spread by rhizomes and stolons. The seeds are dispersed by the water and are capable of germinating throughout the year in favorable climates.
Stems are erect and spreading, with mature plants over 3 feet tall. Some lower stems may be prostrate and are able to root at their nodes. Leaves generally are sessile, attached without stalks and possibly clasping the stem, and are oval to long and lance-shaped. Flowers are produced at the upper ends of the stems with opposing pairs of long stalks arising from the upper leaf axils. Clusters of short flower stalks arise off of these and terminate with the small violet flowers
Characteristicts Important to Control:
A systemic herbicide will be necessary to completely kill all vegetative parts, with new growth likely to occur from some rhizomes or stolons. In areas where excessive moisture can be controlled this will reduce the ability for the plants to grow.