Cuticle development and degree of stomatal occlusion of three Populus clones varied with growth environment and leaf type (early or late leaves). Whereas stomatal occlusion by cuticular components was negligible in plants of all clones grown in a moist controlled environment, heavier cuticle deposition and stomatal occlusion were found on abaxial surfaces of early, but not late leaves, of field-grown clones. Hence these Populus clones responded adaptively to the more xeric field conditions in a fashion that would restrict both stomatal and cuticular water loss. The cuticle around the stomatal apparatus of all clones was ridged, with elaborate stranded patterns emanating from the stomata. Stomatal ledges were found in all clones studied, and ledge aperture was not closely related to pore aperture of the guard cells because of variation in the point of attachment of the ledges to the outer lateral wall of the guard cells. Because stomatal pore and ledge apertures are independent, stomatal impressions (which reproduce ledge aperture only) should not be used to estimate stomatal aperture unless it can be shown that ledges are not present.