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Premise of research. Evolutionary radiations can be driven by physiological tolerances. Protea is a species-rich genus in the Cape Floristic Region of South Africa and provides the opportunity to examine whether drought response traits may have contributed to differentiation in this stress-tolerant genus. Commonly utilized drought responses might be indicative of traits important to species diversification in stressful environments.

Methodology. We studied how greenhouse-grown plants of six white Protea species physiologically responded to drought stress. We measured leaf-level physiological traits such as stomatal conductance, temperature, pubescence, chlorophyll, and abscisic acid (ABA) content.

Pivotal results. Most traits showed similar drought responses across all six species and 29 populations we examined. Only for foliar ABA content, leaf hair density, and foliar chlorophyll content did species respond …