The single species of Prenanthella was usually assigned to Lygodesmia in treatments prior to A. S. Tomb’s (1972b) reassessment. Its base chromosome number of x = 7 was taken as evidence of a possible relationship with Malacothrix, Calycoseris, and Anisocoma, also x = 7 (Tomb 1974). Recent molecular phylogenetic studies (J. Lee et al. 2003) place Prenanthella in a clade with Pleiacanthus, Stephanomeria, and Rafinesquia, all with x = 8. This group, together with Munzothamnus, constitutes the subtribe Stephanomeriinae of Lee and B. G. Baldwin (2004).