Abstract: Wedelia trilobata, a creeping herb native to Central and South America, is one of the world’s 100 worst invasive alien species. It was introduced into South China and has become a noxious invasive weed in agricultural fields, plantations and natural forests. In natural communities, it is observed that the leaves of W. trilobata turn from green to red under high irradiance in summer. The aims of this study were to explore what causes the leaf color change in W. trilobata and what the physiological consequences are. Anthocyanin con-tent was significantly higher in red than in green leaves of W. trilobata, suggesting that the accumulation of anthocyanin at high irradiance was related to the leaf color change. The increased content of anthocyanin contributed to a higher total antioxidant capability in red W. trilobata leaves . Consistent with the higher an-tioxidant capability, decreases in maximum quantum efficiency of photosystem II photochemistry and the effective PSII quantum yield caused by artificial photo-oxidative stress were respectively smaller in red (28.2% and 79.1%) than in green leaves of W. trilobata (70.9% and 93.8%). Leaf color change was not ob-served in native W. chinensis. Our results suggest that the color change may be a physiological mechanism employed by the invasive W. trilobata to acclimate to high irradiance in summer.