Erect perennial with opposite, lanceolate, toothed leaves. We measured a large leaf blade (no petiole) at 6.5 cm long, and 2.5 cm wide. Small white flowers in whorls in leaf axils, flowers measured to 3 mm long. Growth habit is single stemmed, or occasionally branching mid-stem. Square stems are glabrous to sparsely hairy with short hairs. Top of leaves are glabrous, bottom of leaves sparsely hairy with minute hairs.
Very similar in appearance to L. asper. As noted in photo above, L. virginicus has ovate-shaped and blunt pointed sepals, while L. apser has sepals which are narrow and acute.
Habitat is stream banks, swamps, and other wet areas. Checklist of the Vascular Plants of Saskatchewan lists this plant as common. I have only found this plant in the Boreal forest, never south of Greenwater Provincial Park / Hudson Bay.
Height listed in Budd's Flora from 15 to 70 cm, we measured plants to 50 cm tall.
The above photos were taken August 4th, near Hudson Bay about 425 km northeast of our home in Regina, SK.