Abstract Non-adapted plants growing in high altitude such as bracken fern Pteridium arachnoideum are exposed to environmental extremes that may induce a chemical adaptive response. Here we show that there is a non-uniform distribution of low (LMP) and high molecular weight (HMP) phenolics in the frond parts of P. arachnoideum growing at high elevation. LMP–HMP levels were measured in sun-exposed (E) and self shaded (SS) pinnae between 2100 and 3190 m in the tropical Andes, during dry and rainy seasons. While there was no difference in E vs. SS contents of LMP at 2100 m, E accumulated greater LMP–HMP concentrations relative to SS as altitude increased. This difference was increased during the dry season. Linear correlations between the position of each pinnae relative to the ground level and LMP–HMP occurred along a 2570–3190 m transect. Water restriction in the dry season also caused increase of LMP and HMP. We conclude that excess UV-B radiation and water availability are important modelers of the non-adapted plant acclimation response to stress in tropical high mountain habitats.