ORIGIN AND DIVERSIFICATION OF THE CALIFORNIA FLORA: RE-EXAMINING CLASSIC HYPOTHESES WITH MOLECULAR PHYLOGENIES
Article first published online: 7 JAN 2013
© 2013 The Author(s). Evolution© 2013 The Society for the Study of Evolution.
Volume 67, Issue 4, pages 1041–1054, April 2013
How to Cite
Lancaster, L. T. and Kay, K. M. (2013), ORIGIN AND DIVERSIFICATION OF THE CALIFORNIA FLORA: RE-EXAMINING CLASSIC HYPOTHESES WITH MOLECULAR PHYLOGENIES. Evolution, 67: 1041–1054. doi: 10.1111/evo.12016
- Issue published online: 3 APR 2013
- Article first published online: 7 JAN 2013
- Received February 27, 2012 Accepted October 30, 2012
The California Floristic Province exhibits one of the richest floras on the planet, with more than 5500 native plant species, approximately 40% of which are endemic. Despite its impressive diversity and the attention it has garnered from ecologists and evolutionary biologists, historical causes of species richness and endemism in California remain poorly understood. Using a phylogenetic analysis of 16 angiosperm clades, each containing California natives in addition to species found only outside California, we show that CA's current biodiversity primarily results from low extinction rates, as opposed to elevated speciation or immigration rates. Speciation rates in California were lowest among Arcto-Tertiary lineages (i.e., those colonizing California from the north, during the Tertiary), but extinction rates were universally low across California native plants of all historical, geographic origins. In contrast to long-accepted ideas, we find that California diversification rates were generally unaffected by the onset of the Mediterranean climate. However, the Mediterranean climate coincided with immigration of many desert species, validating one previous hypothesis regarding origins of CA's plant diversity. This study implicates topographic complexity and climatic buffering as key, long-standing features of CA's landscape favoring plant species persistence and diversification, and highlights California as an important refuge under changing climates.