Mapping here is tentative. This variable species (2n = 40, 80, ca. 108) is reportedly widespread on damp open sites in southeastern and Atlantic states but uncommon to absent as a wild plant in the Ohio Valley and upper midwest (Cr, K, W). It has been rarely reported from Ky., and all colls. should be rechecked; some plants may be adventive. Also, the species is becoming popular as a planted ornamental pollinator, forming dense clonal patches (missouri botanical garden.org; A. Bush, pers. comm.). The somewhat similar, strictly southern Appalachian diploid (2n = 38, 40), P. montanum Michx., was reported from c. Ky. by Linney (1882) but perhaps based on muticum. See W for distinctions in pubescence and for notes on P. beadlei (Small) Fern., a southern Appalachian species of potential hybrid origin that has been reported close to Ky. (K).. Both muticum and montanum have broad (1.5-4 cm) serrated leaves and relatively loose to reflexed bracts, as in the incanum group (with bilabiate calyx), but they may belong in the pilosum group (with regular calyx). In contrast to the incanum group, their inflorescences are more densely capitate, without evident branches; calyx lobes are relatively short (0.5-1.5 mm), more or less equal, and (at least in muticum) lack distinct apical tufts of long jointed hairs. P. muticum itself also has distinctively short (0-3 mm) petioles.