Origin:
Native to Eurasia, but introduced to North America as a garden and herbal plant. It now is found throughout North America to Alaska, with the exception of the dry southwestern states of Nevada, Arizona, and New Mexico.
Biology:
A perennial that reproduces by seeds, but more commonly it spreads by creeping stems that root at their nodes and by rhizomes. In warmer climates plants remain green throughout the year, while in colder areas foliage dies back and new growth emerges from the roots and rhizomes. Stems are prostrate along the soil, capable of forming dense mats of growth that crowd out other vegetation. A strong mint-like odor is given off by damaged plant parts. A common problem in turf and landscaped areas, especially where shaded.
Identification:
Stems creep along the soil, and are square in cross section, and with backward-directed short hairs on them. Leaves are primarily opposite and are shiny and very slightly hairy. They are round to somewhat oval or heart-shaped, and deeply toothed to scalloped margins. Venation of the leaves is palmate. The flowers occur in the spring on short stems that rise upward. They occur in groups of 2 or 3 flowers arising from the axils of the leaves, and are purple-blue and tubular in shape.
Characteristicts Important to Control:
Due to the underground parts that can grow new plants, a systemic herbicide will be needed to effectively kill this weed. In turf a selective broadleaf product will be needed.
