Vernal pools are ephemeral wetlands found primarily in the Central Valley of California.
Vernal pools have long been noted for containing an evolutionarily rich and unique flora. Plants in the pools must withstand both long periods of inundation and long periods of drought. Implicit in this idea is the assumption that dispersal among pools is limited enough so that factors such as selection and genetic drift may play a role in differentiation among pools. Whether the pool islands that we perceive are indeed genetically differentiated is the question this study addresses. Previous studies of variation in vernal pool taxa are few in number and variable in results.