This largely diploid (2n = 16) member of the palustris complex occurs mostly in northeastern states. Some colls. (especially from HARD) may be referred to the more western E. macrostachya Britt., a polyploid of possible hybrid origin (2n = 38). But this distinction is not clearcut, and both taxa have been combined in some treatments with the European species: E. palustris (L.) Roemer & J.A. Schultes. Further analysis of this circumboreal complex is needed (FNA 23). There has also been some confusion with erythropoda, which was apparently mapped as palustris by BT in BULL and SHEL, and was combined completely by K.