T.I.Chuang & Heckard 1986 - Chuang TI, Heckard LR (1986) Systematics and Evolution of Cordylanthus (Scrophulariaceae-Pedicularieae) (Including the Taxonomy of Subgenus Cordylanthus). Systematic Botany Monographs 10: 1-105. doi: 10.2307/25027622.