Abstract
<jats:p>Ironstone outcrops (Brazilian cangas) are high-elevation environments (> 800 m) characterized by extreme incident radiation, marked fluctuations in water availability, and shallow, oligotrophic soils developing over ferruginous bedrock. Vegetation forms mosaics ranging from exposed rock surfaces to shrub patches and small cloud-forest enclaves (“capões”), generating fine-scale microenvironmental heterogeneity. In these conditions, bryophytes occupy distinct microhabitats where secondary metabolites contribute to stress tolerance. We examined the leafy liverwort Frullania brasiliensis Raddi, a species emblematic of cangas, to assess its phenolic content and in vitro antioxidant capacity. Extracts from twenty populations were analysed for total phenolics and for radical scavenging (DPPH and superoxide anion, O₂⁻). All samples contained phenolic compounds and exhibited antioxidant activity, with notable variation among populations. Superoxide scavenging efficiency increased with relative air humidity, suggesting environmentally modulated metabolic responses. These findings suggest phenolic metabolites may contribute to oxidative stress tolerance in F. brasiliensis in canga habitats and provide a foundation for further research on the functional ecology of bryophytes in rupestrian environments.</jats:p>