Evolution of the Arctostaphylos genus is relatively recent, with hybridization playing an important role; 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. It has been 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.
Present species distribution of Arctostaphylos morroensis is restricted to a very small coastal land area extent on the eastern part of Santa Cruz Island, California. This island is among the northern element of the North Channel Islands in the eastern Pacific Ocean.
- Anne Sands. 1980. Riparian forests in California: their ecology and conservation: a symposium., University of California, Davis. 124 pages
- C.Michael Hogan. 2012. Arctostaphylos. Encyclopedia of Earth. Eds. M. McGinley & C.Cleveland. National council for Science and the Environment. Washington DC http://www.eoearth.org/article/Arctostaphylos
- USFWS. Endangered or threatened status for five plants and the Morro Shoulderband Snail from western San Luis Obispo County, California. Federal Register December 15, 1994.