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Abstract
Helianthus porteri is a sunflower endemic to drought-prone granite outcrops, suggesting that this species possesses some combination of morphological and physiological traits which confer resistance to drought. We compared H. porteri to three other sunflowers from habitats with varying local water availability (H. agrestis, H. annuus and H. carnosus) in a series of experiments with well-watered, sustained mild drought, and soil dry-down treatments. Under well-watered conditions, H. porteri exhibited a root system that allows for greater water uptake per unit mass as compared to the other species. In response to mild drought H. porteri maintained photosynthetic rates while decreasing water loss. Finally, in response to a dry-down H. porteri wilted at a less-negative water potential. Compared to the other Helianthus species, H. porteri possess a unique combination of traits that provide increased water absorption and water conservation, supporting an avoidance strategy for drought resistance.