Across kingdoms, organisms ameliorate UV stress by increasing UV-absorbing pigmentation. Rapid ozone degradation during the 20th century resulted in elevated UV incidence, yet pigmentation responses to this aspect of global change have yet to be demonstrated. In flowering plants, UV exposure favors larger areas of UV-absorbing pigmentation on petals, which protects pollen from UV-damage. Pigmentation also affects floral thermoregulation, suggesting climate warming may additionally impact pigmentation. We used 1238 herbarium specimens collected from 1941 to 2017 to test whether change in UV floral pigmentation was associated with altered ozone and temperature in 42 species spanning three continents. We tested three predictions: First, UV-absorbing pigmentation will increase temporally and be correlated with reduced ozone (higher UV) when accounting for effects of temperature; second, taxa that experienced larger ozone declines will display larger increases in pigmentation; and third, taxa with anthers exposed to ambient UV will respond more strongly than those with anthers protected by petals. Globally, the extent of petal UV pigmentation increased significantly across taxa by ~2% per year. However, temporal change was species specific—increasing in some taxa but declining in others. Species with exposed anthers experiencing larger declines in ozone displayed more dramatic pigmentation increases. For taxa with anthers enclosed within petals, pigmentation declined with increases in temperature, supporting a thermoregulatory role of UV pigmentation. Results document a rapid phenotypic response of floral pigmentation to anthropogenic climatic change, suggesting that global change may alter pollination through its impact on floral color, with repercussions for plant reproductive fitness.

Phenotypic data on ultraviolet floral pigmentation were collected from herbarium records using digital UV photographs of flowers analyzed in imageJ. Code from SAS and R used to run statistics and a tree file used for comparative analyses are provided.