Intraspecific variation providing tolerance to specific edaphic conditions may contribute to population differentiation, speciation, and species coexistence. This process is often examined using reciprocal transplant experiments of closely related species in contrasting edaphic conditions. The two cryptic species Lasthenia californica and L. gracilis occur on a serpentine outcrop in parapatry at Jasper Ridge Biological Preserve. I hypothesized that each species would demonstrate greater fitness in its home range. A reciprocal transplant experiment was conducted in the field to determine home site advantage. Seedlings from each species were planted in both home ranges and in the transition zone where both species occur. Soil was found to vary significantly by outcrop region, particularly with respect to the calcium-to-magnesium ratio. Lasthenia californica performed best in its home range, but L. gracilis demonstrated greater survival and fitness in the transition zone. These findings provided evidence of local adaptation of L. californica to the bottom of the slope where the soil calcium concentration is lower and magnesium concentration is higher, and local adaptation of L. gracilis to the transition zone and the drier top of the slope. Studies on local adaptation using reciprocal transplants are ideal tools for understanding plant evolution and provide valuable information for habitat restoration. link to publication