Leaf morphology and bud-burst variation in Ulmus minor from Italy and France

More than 40 Ulmus minor clones were characterized on the basis of 10 foliar morphological traits and budburst phenology in two successive years. Ramets, 4- and 5-years-old, were obtained by means of self-rooted cuttings from elms located in northern, central and southern Italy and in France. Measurements were taken in an open field in the vicinity of Florence (Italy). The morphological traits were found not to be appropriate for describing the variability between clones of different origins, even if some of these traits indicated a xeric adaptation in clones originating from southern Italy. On the contrary, the phenological traits were valid describers of the origin of the clones. Indeed, the southern-Italian clones flushed earlier than the others, while the French clones were more delated. A comparison of the results of the two years showed that the chilling requirements on the trial site were not satisfied. The actual state of knowledge regarding dormancy in the Ulmus genus does not enable to speculate further on the results of this research. Morphological characters seem to show a greater phenotypic plasticity with respect to phenological traits.