Sandquist, D.R., and J.R. Ehleringer. 1997. Intraspecific variation of leaf pubescence and drought response in Encelia farinosa. Genetic differentiation associated with contrasting desert environments. New Phytol. 135:635-644.

Traits associated with leaf energy balance are especially important for desert plants because decoupling leaf and ambient temperatures can be critical for maximizing productivity and survival in these hot and dry regions. Deserts are also one of the most climatically unpredictable and heterogeneous biomes, thus, variation of energy balance characters due to either plasticity or genetic differentiation may also be crucial for the success of desert plant species. In a common environment, we examined variation in the traits associated with energy balance and productivity in Encelia farinosa A. Gray (brittlebush) plants. Comparing two populations from contrasting rainfall and drought climates we found that plants from the wetter population (Superior, Arizona) always maintained higher leaf absorptances than plants from the more xeric region (Oatman, Arizona) when at similar water potentials. Superior plants also increased stomatal conductance and photosynthesis in response to mid­spring rainfall whereas Oatman plants did not. Oatman plants, however, tended to have greater leaf areas and continuous spring growth which resulted in larger sizes relative to Superior plants, yet both populations produced the same number of flower heads. The differences for these traits, and the associations among them, agree with predictions based on the contrasting drought and rainfall environments of these two populations. Our results suggest that the differences may represent alternative suites used for maximizing carbon gain over the climatically variable range of this widespread species. Furthermore, these results, having been found under common environment conditions, suggest that these differences may have some heritable genetic basis, and this may contribute to a greater potential for local adaptation in this species.