This southeastern taxon may be more frequent in Ky. than the largely midwestern var. rigidum, but more critical review of colls. is needed. The more western var. humilis (Porter) S.B. Heard & Semple is virtually unknown east of the Mississippi and Ohio Rivers (FNA 20); it has been treated as S. canescens (Rydb.) Friesner by W. Distributions of the three taxa overlap considerably and there appears to be some intergradation, but var. glabratum appears to be more restricted to rocky glades than var. rigidum, which is locally common in remnants of taller grassland on deeper soils. Var. glabratum has also been treated as a subspecies (FNA 20) or as a species (F, K, W): S. jacksonii (Kuntze) Fern. W has distinguished var. glabratum (S. jacksonii) as follows: outer series of phyllaries glabrous on the back (versus pubescent), glabrous to short-ciliate on the margin (versus short-ciliate); leaf undersurface glabrous to somewhat hispid with 0-20 hairs per square mm (versus hispid with 7-50 hairs per square mm) the margins and midrib beneath often more densely pubescent; stems glabrous to somewhat hispid with 0-25 hairs per square mm (versus slightly to strongly hispid with 10-70 hairs per square mm). Also, It is generally less robust, with smaller inflorescences that usually containing 15-45 heads (versus 30-120), and that tend to be more rounded. leaves tend to be narrower, the larger ones usually 1-5 cm wide (versus 2-10 cm); and reported 2n = 18 (versus 18 and 36).