This is widely scattered in marshes and shallow waters of southeastern states and the Great Lakes region, including older man-made ponds. Its known distribution has curious gaps (K), perhaps suggesting association with less eutrophic waters. Populations can abruptly disappear, perhaps due to pollution (E. Hartowicz, pers. comm.). At least some colls. from Ky. (e.g. BELL & TRIG) are referable to var. crassior Fern., but that variety has not been distinguished from the more southeastern var. quadrangulata in recent treatments. The related species, E. equisetoides (Ell.) Torr., occurs mostly on the southeastern and Atlantic Coastal Plain, but also occurs in the Great Lakes area. It is known from most states around Ky. and it should be expected, especially on lowlands. Culms are transversely nodose-septate, appearing jointed (versus not so), about 5-9.5 mm in diameter (versus 1-5.5 mm).