Mechanisms of plant protection and acclimation to potentially damaging solar ultraviolet-B (UV-B, 280-320 nm) radiation incident on the Earth's surface were examined in Oenothera stricta. Attenuation of this radiation in the upper leaf epidermis reduces the penetration of UV-B radiation to the mesophyll where damage to physiologically sensitive targets can occur. The epidermis is a highly selective targets can occur. The epidermis is a highly selective radiation filter that can attenuate up to 95% of the incident UV-B radiation and yet transmit between 70% and 80% of the visible radiation. Photosynthetic rates of leaves exposed to UV-B radiation were not significantly reduced at dose rates representative of the radiation flux found in the habitat of this species, but significant photosynthetic depression was observed at dose rates that exceed the field UV-B flux.