The genus is situated in a monphyletic clade or sub-family known as the Arbutoideae, which is populated by taxa having bright fleshy berries with fibrous or bony endocarp. Evolution of the genus is relatively recent, with hybridization playing an important role, especially in non-crown sprouting taxa; however, convergent evolution patterns appear to complicate cladistic constructions for certain portions of the genus cladogram. In any case, fossil ancestors of the Arctostaphylos genus have been suggested to have occurred in the Middle Miocene, with modern species beginning to take shape in the Late Tertiary. Sands has further posited that in the earlier Tertiary a greater species diversity was present, influenced by influence of floristic influence of southwestern North America ancestors. This hypothesis also suggests that the present palette of California Arctostaphylos species became more depauperate upon arrival of a cooler drier climate in the Late Tertiary.These evolutionary views are coincident with other research that points to fire-dependent plant associations developing in the Late Miocene in California.
Earlier taxonomic treatments were governed by morphological methodology, most notably by Wells; however, more recent genome sequencing work by Boykin et al. has demonstrated the incongruence of purely morphological treatment with closely related species as determined by Internal Transcription Sequencing (ITS) methodology.
- C.Michael Hogan; World Wildlife Fund. 2012. ''Arctostayphylos". Encyclopedia of Earth, National Council for Science and the Environment, Washington DC Topic ed. M.McGinley
- Peter H. Raven and Daniel I. Axelrod. 1978. Origin and relationships of the California flora. University of California Press. 134 pages