Figure 2. Pigmentation patterns can provide defence against herbivores and environmental conditions.

(A) The flower of St John’s wort (Hypericum calycinum) produces a UV bullseye that could participate in pollinator attraction (UV absorption) and provide chemical defence (DIP production) against the caterpillar herbivore of the Bella moth. (B) The flowers of silverweed cinquefoil (Argentina anserina) appear yellow to the human eye but produce a UV bullseye. The size of the UV absorbing region can vary between populations: individuals growing at lower latitudes or higher altitudes tend to form larger bullseyes. If big enough, the bullseye can effectively shield pollen grains against damage caused by UV irradiance: incident UV rays are absorbed by the bullseye centre instead of being reflected on the pollen-producing anthers in the centre of the flower. The percentage of viable pollen grains following UV treatment was found to increase with bullseye size, supporting a protective role for petal pigmentation patterns. Image credit in (A) JJ Harrison via Wikimedia Commons and in (B) Dr Matthew H. Koski.