Olea europaea L. is one of the most widespread tree crops in the Mediterranean Basin and the high genetic and phenotypic diversity of cultivars reflects the long evolutionary history of the species in the region. We assessed the intraspecific variability of 83 olive cultivars from different Mediterranean countries, by screening leaf and stem traits involved in plant water-use strategies. The trees were maintained in the worldwide olive germplasm bank of Marrakech (WOGBM), Morocco, and in the French olive Germplasm bank of Porquerolles Island (FOGB), France. Our results showed a considerable phenotypic variability among the varieties within each of the collections, which is partially related to the genetic group ('Eastern', 'Western', and 'Central' Mediterranean Basin and 'admixed') to which each variety can be assigned. Significant differences in average trait values between the two collections were also found for certain traits. Trees maintained in the WOGBM were found to be more conservative, showing higher leaf mass per area, leaf dry matter content and wood density. Our study brings new insights as to how traits of olive cultivars differ among genetic groups. This will allow one to identify the most relevant traits to use for an easy and quick screening of olive germplasm in the broad perspective of sustainability of the olive sector in the Mediterranean Basin.