This is widespread across eastern states in native grassland on dry or damp sites, usually with somewhat inferttile or medium acid soils. It is generally absent from the Bluegrass region but it can persist in artificially established grassland on poorer soils (e.g. at Flora Cliff in FAYE). IThe species may vary significantly in leaf width, pubescence, chemistry and cytology (Chambers 1993; pers. obs.). It can generally be distinguished from congeners in Ky. by its sharp-tipped calyx lobes (versus acuminate to deltoid), and narrow leaves (mostly 2-5 mm versus 3-15+ mm). Also, tenuifolium is largely glabrous, unlike congeners, but a few colls. from Ky. have stems hairy at least on the angles. Both diploids (2n = 40) and tetraploids (2n = 80) are known across its range (W). However, segregates have not generally been recognized. Hybridization with other species is not documented, but occasional plants with more pubescence or broader leaves suggest transitions to pilosum; see also notes under torreyi and virginianum. There has been nomenclatural confusion with P. flexuosum (Walt.) B.S.P., with longer rigidly awned calyx teeth (2.3-5 mm) and broader leaves; that species occurs further south, mostly on the Coastal Plain (W).