M. aurantiacus is one of a small group of about eight species of woody perennials which are now usually placed in Mimulus but have, by some authorities, been treated as a separate genus – Diplacus; all the species in this group are natives of western N. America. The genus Mimulus, with about 150 species, consists mainly of annuals and herbaceous perennials and is richly represented in western N. America (seventy-six species are treated by Munz in A California Flora); it also occurs in S. America, Africa, Asia, and Australia.
The standard work on the Diplacus group, is: H. E. McMinn, ‘Studies in the Genus Diplacus’, Madroño, Vol. 11 (1951), pp. 33-128.