This species is widespread on acid soils across eastern North America, except in the upper mid-west, and there is significant variation; 2n = 18, 36, 54 (Cr, FNA 20). Separation of var. rugosa (largely diploid) versus var. aspera (largely tetraploid) remains somewhat provisional in Ky. and needs further checking. Some colls. have been referred to var. villosa (Pursh) Fern., which may be transitional to var. aspera. Colls. from HARL (EKY) and perhaps MCRE (KY) are at least transitional to the largely glabrous northeastern var. sphagnophila Graves, but further review is needed before definitie mapping. Distinction of rugosa from ulmifolia is sometimes difficult, both being highly variable species. S. rugosa has elongate creeping rhizomes forming dense stands of solitary stems (versus short rhizomes or caudices with stems often paired); leaves are slightly to strongly rugose-veiny (versus not at all) and subsessile (versus short-petiolate to subsessile); flowering heads have (4)6-8(12) rays (versus 3-6).