This is known only from calcareous clifftops in the southern Ridge & Valley of Ga. and Tenn., and in disjunct areas along or near the western edge of the Cumberland Plateau in Ky. Sm treated this as a species along with other segregates of fulgida, and a modified version of his treatment is accepted here (Campbell & Seymour 2013). R. truncata is close to missouriensis (see notes under that name), but generally distinct in its mostly glabrous stems and leaves (versus densely villous-hirsute), broader lower leaves mosrly 1.5-3 cm wide (versus 1-1.5 cm) and dentate to entire (versus entire); flowering branches mostly spreading (versus ascending); paleae usually greenish to brownish or darker, grading into blackish veins (versus pale whitish green with sharply contrasting blackish veins), and rays mostly 8-20 mm long (versus 15-25 mm). B's coll. (NY, #2630, 8 Sep 1939) from Cox Bend in PULA was annotated by Cronquist as "correctly identified with R. truncata but no more than a variety, at best, of R. fulgida." Ky. plants appear similar to the type (NY): J.K. Small, 6-12 Aug 1895, along the Chickamauga Creek near Ringgold, Catoosa Co., Ga. Small (1898) noted that truncata occurs "in the northwestern and little explored part of [Ga.]... quite common in the limestone districts". The species should be searched for further in Ga., Tenn. and Ala. along limestone cliffs around the southern Cumberland Plateau and Ridge & Valley region (where recently found by A. Floden in Campbell Co., Tenn.). However, variation within the species may be significant: initial flow cytometry by P. Zale has indicated triploid condition in a Ky. plant but diploid (2n = 38) in a Ga. plant (Campbell & Seymour, 2013). With some biogeographic parallels, cryptic variants may also exist among associated xerophytic calciphiles in Sedum, Mononeuria, Cerastium, Houstonia, Allium and Sporobolus.