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. Rafinesque (1828-30, 2: 264) noted that his S. rugosum Raf. (a synonoym) was "called Muskrat weed, because muskrats feed on it, and Indians bait the traps with it." Sium may be a basal member (with 2n = 12) of a complex clade that is concentrated in wetlands and partly poisonous: including Cicuta (2n = 22), Oxypolis (28-32), Trepocarpus (18) and Ptilimnium (14-32).