Several poplar species within a section, but also between sections, are cross-compatible, thus a high number of interspecies-hybrids occur naturally or have been artificially produced during the last 100 years. Very often, systematically kept records on the production or vegetative propagation of poplar hybrids and/or clones have not been available to date. Hence the origin of the poplar plant material used for the generation of hybrids or clones is not quite clear in many cases, thus making the differentiation between the clones a difficult task. Therefore, genetic markers are needed to clearly identify and differentiate the species and hybrids in the genus Populus, including both identification of existing clones and the breeding of new ones. One aspect of this study is therefore to develop molecular markers for the identification and differentiation of species, hybrids, and clones of the genus Populus.