Habitat replacement and fragmentation associated with projected climate change pose a critical threat to global biodiversity. Edaphically limited plant species with restricted dispersal abilities will be especially handicapped to track their optimal climate spatially. Instead, the persistence of these species will depend on their capacity to adapt in situ to novel climate regimes. Here I evaluated the evolutionary potential of Lasthenia fremontii, an annual plant species restricted to ephemeral wetlands called vernal pools in California to adapt to the projected patterns of climate change. Across L. fremontii distribution there is a latitudinal gradient in precipitation which, combined with reduced gene flow rates, might be driving adaptive divergence in climate tolerances among populations of this species. Accordingly, I estimated (1) the spatial distribution of genetic variation and gene flow across the species range, (2) the extent to which the climate variability experienced by the vernal pools has selected for seed dormancy in L. fremontii populations, and (3) the degree of local adaptation and additive genetic variation in response to a simulated spectrum of precipitation conditions. My analyses revealed an isolation-by-distance model of genetic differentiation among vernal pools and a low to moderate degree of genetic differentiation among pools within a single complex. Germination time was faster in the northernmost (historically wettest) population than in the southernmost (historically driest) population but with mixed responses in others. I observed a significant positive relationship between the historical variability in autumn precipitation and extent of seed dormancy in a population. These findings were consistent with the patterns of adaptation to local rainfall conditions observed among three of the populations reciprocally exposed to local but extreme precipitation conditions. Unexpectedly, however, populations expressed higher levels of additive genetic variation but reduced fitness under extreme drought events in comparison with moderate and extreme rainfall conditions. Further, both peripheral populations expressed optimal fitness in their native conditions but the central population did not. Taken together, these results revealed that restricted gene flow, coupled with differences in the history of local selection pressures, have led to significant divergence in the climatic tolerances and relative evolutionary potential of populations. Contrary to intuitive expectations, central range populations with less predictable climate regimes may not preserve adaptive potential for more extreme environments. That potential may only be present at the current environmental extremes
