The genus Echinacea, indigenous to North America, belongs to the aster family (Asteraceae) and includes nine different species (Anon. 1997a). Of these species, E. purpurea, the purple coneflower, is both most commonly used as a medicinal herb and intensively studied. Less popular species of the genus include E. pallida, the pale purple coneflower, and E. angustifolia, the narrow-leafed purple coneflower (Foster 1997, Anon. 1996).
According to one source, "Echinacea seems to have been used as a remedy for more ailments than any other plant" (Anon. 1997a).