1. Switch from specialized to generalized pollination
2. 2D.I. Axelrod, 1980 . Contributions to the Neogene Paleobotany of Central California . In:University of California Publications in Geological Sciences, V. 121.Los Angeles, California. The University of California Press.
3. 3D.I. Axelrod, 1989 . Age and origin of the chaparral . In:Symposium on Paradigms in Chaparral Ecology, Los Angeles California USA(S. Keeley, ed.), Natural History Museum of Los Angeles County Science Series, no. 34.