Photosynthetic pigments and several structural characteristics were measured in leaves of Andropogon gerardii from tallgrass prairie populations in an unburned, low-irradiance site and a burned, high-irradiance site to determine if these species displayed sun/shade differences similar to those documented in forest species. Early in the growing season, leaves of A. gerardii in the low-irradiance, unburned site had significantly lower stomatal density, pore length, and conductance, as well as specific leaf mass and thickness than leaves from the high-irradiance, burned site. Moreover, the chlorophnyll a:b ratio, carotenoid content, and bundle sheath-vascular complex area were significantly lower, but chlorophyll content (mass/mass) was greater in leaves in unburned vs burned sites. These differences are consistent with sun/shade adaptations reported for forest understory plants and may contribute to the low productivity of A. gerardii in unburned tallgrass prairie