Bigtooth and trembling aspens (Populus grandidentata and P. tremuloides) typically occur in Michigan and throughout much of their native range in natural clones of several to many genetically identical individuals. A clone is initiated by the establishment of a seedling (the ortet); suckers (ramets) arise from the root system of the ortet. Death of ramets and decay of root connections may result in formation of several independent root systems within the same clone. Average size of individual clones of both species on the research sites in Michigan was approximately 0.07 acre. Male and female clones did not differ in size. Clones are established, expand, intergrow, and coalesce depending upon the ease of seedling establishment, rapidity of root expansion, inherent suckering ability, and amount of disturbance. Although the aspens are typically recognized as pioneer species, they may be more permanently part of the habitat than most of their non-clonal associates. Recognition of the clonal structure of most aspen stands is important in many aspects of research.