Galeopsis tetrahit L.
Common hemp-nettle is native to Europe and Asia, now widespread and often considered invasive in North America.
Identification: Plants are 6-28" (15-70 cm) tall, with branched stems that have hairs that are bent backward (retrorse). Leaves are opposite, with stems about ⅜-1" (1-2.6 cm) long, elliptic to ovate, 1-4" (3-10 cm) × ⅜-1¾" (1-5 cm). They have short stiff hairs and crenate edges. Flowers are tubular and bilaterally symmetrical, appearing from June to September. They are purple with white centers or white with pink/purple centers, or just plain white.
Galeopsis tetrahit on Missouriplants.com
Galeopsis tetrahit at the University of Wisconsin-Green Bay Cofrin Center for Biodiversity
Galeopsis tetrahit on biology.burke.washington.edu
Galeopsis tetrahit on Invasive.org, Center for Invasive Species and Ecosystem Health
Galeopsis tetrahit on luirig.altervista.org
Galeopsis tetrahit on Discover Life
Galeopsis tetrahit on Plants for a Future, a resource and information centre for edible and otherwise useful plants
Galeopsis tetrahit on michiganflora.net
Galeopsis tetrahit description by Thomas H. Kent, last updated 31 Oct 2013.