High β diversity in the flora of Californian serpentine 'islands'
Identification of global biodiversity hotspots is a leading conservationpriority ( Hotspots.Conservation International, Washington, DC; Precious Heritage: The Statusof Biodiversity in the United States. Oxford University Press, Oxford, UK), but weknow little about the nature and structure of such hotspots. Botanical richnessin one recently identified hotspot, the California Floristic Province, has longbeen attributed by evolutionists to edaphic and climatic heterogeneity. Here we demonstrate that the flora restricted (endemic) toserpentine soil, the state's most botanically distinctive substrate, showsunusually high 'β diversity' – i.e., spatial variation inspecies composition – among regions, although 'α'diversity within any given region is low. Conservation of an endemic-rich florarequires a network of sites to capture this among-region or spatial component ofdiversity.