This is widespread in most of North America (K), but it is uncommon to absent in much of the Ohio Valley and in mid-western states (somewhat complementary to grayi). It typically occurs on seasonally wet acid soils, including streamhead seeps. The coll. from GREE (EKY) has pubescent perigynia like grayii, but in other characters it seems to match intumescens (as det. by R. Naczi). Some plants in more acid seeps on the Cumberland Plateau of Ky. and Tenn. may be a distinct segregate. These have spikes with relatively few perigynia, on long stems that decline or droop, and relatively narrow leaves (D. Estes & A. Floden, pers. comm.). Such plants have been collected from BELL, HARL, LAUR, LETC, JACK, MCRE, POWE, PULA, RUSS and WOLF (EKY).