Abstract:Variation in the ultrastructure of leaves of Polygonum viviparum L. grown at three different elevations (2500 m, 3200 m and 3980 m) was observed with the aid of an electron microscope. These observations revealed strong differences in chloroplasts ultrastructure between plants growing at different altitudes. A tendency was observed for chloroplasts to increasingly concentrate at the center of cells as elevation increases, presumably a form of protection from intensifying irradiation. The number of thylakoids per chloroplast and the degree of thylakoid stacking were both also observed to decrease with increasing elevation. This probably represents a strategy to reduce excess light absorption. Thylakoid swellings, a result of environmental stress, were observed in the chloroplasts of leaves from all three elevation levels. A positive association was Observed between increasing elevation and observed levels of chloroplast deterioration. Appressed membranes in grana were observed in the residual thylakoid pieces in these damaged chloroplasts. It is suggested that chloroplasts with greater membrane stacking were more susceptible to damage from high irradiation.