A European native, well known as a common and troublesome tap-rooted weed across North America. Collected by D. Cooley as early as 1837, probably in Macomb Co., and now found throughout in both moist and dry ground, thriving in disturbed places, along roadsides, in fields, and also in more natural habitats such as streamsides, in clearings in swamps and forests, and on shores.

Many of our plants have a well-developed “grain” on only 1 of the 3 inner tepals [f. unicallosum Peterm.] The inner tepals vary from entire to shallowly toothed, both types of margin often being found on the same plant, sometimes even on the same fruit. Hybrids with R. obtusifolius [R. ×acutus L.] occur occasionally. Apparent hybrids have been seen from Berrien, Houghton, Ingham, and Macomb Cos. and North Manitou Island (Leelanau Co.), and doubtless occur elsewhere.