In its broad sense, S. caroliniana Walt. occurs mostly in Atlantic states from Ga. to N.H., but there are also somewhat disjunct populations further west as far as in the Ozarks on Mo (K). Potential segregates remain rather poorly understood. As a species, subspecies or variety wherryi is restricted to disjunct regions of s. Ohio, c. Ky., c. Ala., s. Mo and perhaps elsewhere (F, FNA 5, W, SERNEC). In Ky. it occurs on limestones and on black acid shale. A few colls. from ROWA and MONT (KY) may be transitional to the northeastern S. pensylvanica Michx., which reportedy differs as follows: calyces glandular-pubescent (versus with long, straight, nonglandular pubescence), 1.5-2.2 cm long (versus 1-1.8 cm). Both taxa have been combined as varieties or subspecies with the strictly southeastern S. caroliniana Walt. (sensu stricto), but treatments have been inconsistent and further revision is desirable. Recent molecular analysis indicates that these three taxa are about as distinct from each other as they are from virginica, with which they can hybridize (Burgleigh & Holtsford 2003). The caroliniana complex is relatively unspeciaized for particular pollinators, but large bees and, to a lesser extent, hawkmoths appear to be the most frequent visitors; hawkmoths appear to be relatively efficient pollinators (Reynolds et al. 2009).