Hybridization can occur between all three taxa.
There is insufficient information on the extent of gene exchange and its relevance for evolution and diversity of the complex consisting of these three taxa. In the course of investigations on morphological, genetical, and ecological differentiation the authors found that the types of trichomes occurring on shoots and leaves are species specific. They can thus be used for identification of hybrids. Using this feature it was possible to do population studies which showed that on some habitats north of the Alps q. pubescens and q. petraea form hybrid swarms over a large area. At present the genetical variability of the complex is being analyzed by means of isozymes with emphasis on correlations between genetical, morphological, and ecological variation.