In this paper we carried out a comparative analysis of three alliances, namely Quercion petraea, Betonico-Quercion and Lathyro-Quercion, which span Central and Eastern European thermophilous oak forests. The main goal was to find out floristic and ecological differences as well as to assess specificities in the phytosociological and layer structure across the syntaxa in different regions of Europe. Cluster analysis was performed based on the Bray-Curtis distance matrix and the flexible beta algorithm. A phytoindication method was applied to determine ecological relationships. Variability in the phytosociological structure was studied by shares of species of different classes of vegetation. The layer structure features were investigated by comparing species with the highest constancy value within each layer. Analysis of the distribution boundaries of differentiating species allowed the geographical boundaries of the three identified syntaxa clusters to be delineated. In the phytosociological structure, the greatest differences were found in the proportion of species of Quercetea pubescentis and Brachypodio-Betuletea classes. The Central and Eastern European syntaxa groups were shown to be significantly different in the constancy-ranked series of major layer-forming species.
