This subaquatic plant is widely scattered over temperate regions of North America, but generally restricted to relatively undisturbed marshy meadows and thin swampy woods. In Ky. it is rare and usually occurs in the margins of sloughs along larger streams and rivers. It may be a basal member (2n = 12) of a complex clade that is wetland-concentrated and somewhat poisonous: including Cicuta (2n = 22), Oxypolis (28-32), Trepocarpus (18) and Ptilimnium (14-32).