Coefficient of Conservatism:
Coefficient of Wetness:
Disturbed ground, shores, and river banks. Considered native in North America, but like other of our weedy species, apparently not so in Michigan where first collected in 1894 in Bay Co.
Our only collection of var. humile (Hook.) S. Watson, a prostrate form with smaller leaves (less than 2.5 cm) and heads, is from disturbed ground at Ann Arbor, Washtenaw Co. In var. humile the seeds are 0.8–1 mm broad and the leaves entire or nearly so, while in the generally large and erect var. rubrum the seeds are only 0.6–0.8 mm broad and the leaves coarsely toothed or sinuate.