The ecophysiological and biochemical traits of Calamagrostis epigejos (Roth.) Festuca rubra L. and Oenothera biennis L. growing on two fly ash lagoons of different weathering stage (L1-3 years and L2-11 years) of the “Nikola Tesla- A” thermoelectric plant (Obrenovac, Serbia) were studied. Species-dependent variations were observed at the L1 lagoon; the greatest vitality (Fv/Fm and Fm/Fo) followed by higher photopigment and total phenolic contents were measured in O. biennis in relation to C. epigejos (p<0.001) and F. rubra (p<0.001). At the L2 site, higher vitality was found in O. biennis (p<0.001) and F. rubra (p<0.01) compared to C. epigejos. O. biennis had the highest photosynthetic capacity. The results obtained in this study indicate that all examined species maintained a level of photosynthesis that allowed them to survive and grow under the stressful conditions in ash lagoons, albeit with lower than optimal success. [Projekat Ministarstva nauke Republike Srbije, br. 173018]