Introduced from Europe where it has been used medicinally for centuries. Subsequent leaves opposite, oval to elliptic, increasingly larger. Underside leaf margins dotted with a few elevated black glands. Stems with numerous sterile shoots 2-10 cm long from the lower leaf axils, highly branched near the top, glabrous, often reddish, with black glands along 2 longitudinal ridges. Edges of leaf lower surfaces lined with elevated black glands .
Fragmented rhizomes can develop new plants.
Under favorable conditions, roots grow deeper and fewer rhizomes develop. Petals 5, separate, 8-12 mm long , typically dotted with black glands along the margins. Stamens yellow, numerous . Styles 3, 3-10 mm long . Plants typically do not flower the first year.