Our studies investigated UV-B radiation effects and their interaction with drought stress in the important New Zealand pasture legume white clover (Trifolium repens L.). Population studies showed intraspecific differences in UV-B responsiveness. Slow-growing white clover ecotypes adapted to other stress factors were tolerant to UV-B, whereas UV-B sensitivity was observed in productive white clover cultivars. Plants exposed to drought showed decreased UV-B sensitivity, resulting in beneficial interaction effects between these stress factors. Levels of protective flavonoid pigments were highest in the stress-tolerant white clover ecotypes and in the combination of UV-B and drought. The results emphasise roles for flavonols in UV-B tolerance, both on a population level and in conferring cross-tolerance via other stress factors.