Photosynthesis and water efflux were measured in different PAR and stomatal conductance in members of Avicenniaceae and Rhizophoraceae. Trend of leaf temperature with irradiance and its effect on photosynthesis were also estimated. In most of the studied species, photosynthesis and stomatal conductance followed similar trends with increase in irradiance. The rate of net photosynthesis and stomatal conductance were higher in members of Avicenniaceae than in Rhizophoraceae. In Avicenniaceae, the optimum PAR for maximum photosynthesis ranged between 1340-1685 ${mu}mol;m^{-2}s^{-1}$, which was also higher than that of Rhizophoraceae (840-1557 ${mu}mol;m^{-2}s^{-1}$). Almost in all the studied taxa, transpiration and stomatal conductance followed similar trends and reached the maximal peaks at the same PAR value. The range of breakeven leaf temperature was almost the same in both the families ($34-36^{circ}C$ in Avicenniaceae and $33.5-36.3^{circ}C$ in Rhizophoraceae), beyond which assimilation rate declined.