PCA of relevés of alluvial/waterside Po Plain and karstic Ulmus minor-rich forests and Fraxinus angustifolia subsp. oxycarpa swamp forests of Frangulo-Fraxinion (First component: 18.31 % of total variance, second component: 11.83 %). Relevés are grouped and labelled according to the dendrogram of Fig. 5. A: Polygonato-Quercetum roboris; B: Salvio glutinosae-Quercetum roboris ass. nov.; C: Vinco minoris-Ulmetum minoris ass. nov.; D: Lamio-Ulmetum minoris; E: Rhamno catharticae-Ulmetum minoris ass. nov.; F: Valeriano-Fraxinetum oxycarpae; G: Cladio-Fraxinetum oxycarpae.