Polymnia johnbeckii, a new, narrowly endemic species, is distinct in its combination of highly dissected leaves, hirsute herbage, and relatively large, showy heads. It is known from two populations in Marion County, Tennessee, and should be considered a rare species at both the state and federal level. A chromosome count indicates that P. johnbeckii is diploid. Although standard cladogenesis is the null hypothesis for the origin of this diploid species, evidence supporting an alternative scenario of homoploid hybrid speciation is discussed.