The nature and extent of phenological variability among individuals of sumac, Rhus glabra, was investigated. The phenological events considered are: bud elongation, bud opening, leaf appearance, cessation of leaf and twig growth, inflorescence appearance, first flower and fruit, and cessation of inflorescence growth. The sex of the clone, height of the stem above ground, age -of the stem, and the final twig length showed association with phenological events. Phenological stages are grouped into the cessation events which develop slowly throughout the clone, and the developmental events which occur rapidly throughout the clone. Through the use of a multiple range test, the mean values of all clones for each event can be grouped into those which show no statistical difference from each other. The number of times one clone is grouped with another may be considered an index of the phenological similarity of the clones. The major conclusions drawn are: (1) the phenological variability appears to be primarily associated with the genetic constitution of the plant; (2) aspects of the structure and life history of the clone seem associated to a lesser extent with its phenology; (3) exposure of the clone on the hilltop and exposure of the stem within the clone seem to have no effect on the phenology.