This tetraploid (2n = 48) is largely restricted to limestone glades of the southern Interior Low Plateaus, mostly in Tenn. but also in Ala. and Ky. (FNA 4, K). Small disjunct populations have also been reported from the Ozarks of northern Ark. and the Cretaceous limestone of north-central Texas (Swadek 2012). The species is probably derived from the southwestern P. calycinus (Engelm.) Kiger, which has diploid and tetraploid races (Murdy & Carter 2001; FNA 4). In Ky. the species is known only from small populations ar Flat Rock Glade in SIMP, where it has declined, and at the Russellville Glade or nearby in LOGA. Causes of decline are not obvious, but there may be some potential for disturbance from mowing, burning or browsing to improve conditions, if applied during the dormant season. Even in the cedar glades of Tenn., the species appears to be declining without active management, but it prospers locally along more disturbed roadsides (P. Adanick, pers. comm.). It is possible that there is also some removal of plants, since the genus is becoming popular for succulent ornamentals (P. Adanick, pers. comm.).