Morpho-anatomical leaf traits and photosynthetic activity of two alpine herbs, Podophyllum hexandrum (shade-tolerant) and Rheum emodi (light-requiring), were studied under field (PAR>2 000 µmol m-2 s-1) and greenhouse (PAR 500 µmol m-2 s-1) conditions. Mesophyll thickness, surface area of mesophyll cells facing intercellular spaces (Smes), surface area of chloroplasts facing intercellular spaces (Sc), intercellular spaces of mesophyll cells (porosity), photon-saturated rate of photosynthesis per unit leaf area (PNmax), and ribulose-1,5-bisphosphate carboxylase/oxygenase activity decreased in the greenhouse with respect to the field and the decreases were significantly higher in R. emodi than in P. hexandrum. P. hexandrum had lower intercellular CO2 concentration than R. emodi under both irradiances. The differences in acclimation of the two alpine herbs to low irradiance were due to their highly unlikely changes in leaf morphology, anatomy, and PNmax which indicated that the difference in radiant energy requirement related to leaf acclimation had greater impact under low than high irradiance. and S. Pandey, N. Kumar, R. Kushwaha.