Mapping is tentative due to much past confusion with juncea and gigantea. S. missouriensis is a widespread variable species, centered in the Great Plains (perhaps on relatively base-rich soils) but with disjunct populations reported as far east as se. Tenn. and nw. Ga, (D, F, Cr, W, Y; FNA 20). In Ky., there are few verified colls. and the species may be largely restricted to the Coastal Plain (Jackson Purchase) and adjacent hills. S. missouriensis is close to juncea (typical of acid soils), and some plants in Ky. may be hybridized; 2n = 18 in both species within eastern states. It can also be confused with gigantea if basal leaves have withered. In missouriensis, rhizomes are more slender and widely spreading than in juncea. Larger leaves generally have 3 main veins (versus one dominant); basal leaves are narrower (mostly 1-2 cm versus 2-7 cm); uppermost primary leaves tend to be smaller (ca. 2-10 mm wide versus 5-10 mm) and more reduced into the inflorescence. Its inflorescence branches are acutely ascending to arching; those of juncea are widely ascending to arching to recurved. Intraspecific taxonomy remains uncertain. Plants in Ky. are probably all referable to the largely midwestern var. fasciculata Holz, which is relatively robust but has small achenes with little pubescence. The coll. mapped here from EDMO (US) was initially misidentified by Davies (1955) as the closely related S. gattingeri Chapman, a less rampant, smaller-headed plant that is known only from the Ozarks of Ark. and Mo., plus a few disjunct sites in c. Tenn.