The three-dimensional characteristics of canopy structure and light environment of clones of a common tallgrass prairie species, Andropogon gerardii (big bluestem), were analyzed in native and reconstructed prairies near Ames, Iowa to determine if clones are limited in size by the effects of self-shading. Clones tended to be nearly circular, with a mean circumference of 158 cm and a mean cross-sectional area of 2060 cm²; clone height was consistently near 60 cm in early summer. Irradiance at a given height in the canopy, calculated as a fraction of radiation above the canopy, decreased rapidly during May and June as plants completed most of their seasonal growth, but was relatively constant in July and August. A vertical gradient in light dominated the spatial variation in light within clones. Horizontally through a clone, light levels were higher around the southern (sun-side) periphery. Spatial variation in light, in terms of the range of values found, was least at the bottom and upper parts of the canopy and greatest in the middle of the canopy. Leaf mass/area and total leaf area per increment of canopy height were highest at 30 cm below the top of the canopy and were lower at 15 cm and 45 cm below the top of the canopy. Mean leaf area index of clones was 6.58. Diameter of clones had a weak effect, if any, on the light environment within a clone. Only clones with diameters of <20–30 cm are likely to have substantially less self-shading than larger clones. Competition with other plants or limitation by other morphological constraints, rather than limitation by self-shading, may control the upper size limit of clones.