Morphological variability of fruits and leaves allows delimitation between cultivated and wild chestnuts and their natural crosses

North Adriatic sweet chestnut (Castanea sativa Mill.) orchards are unique as in a relatively small area three different genetic groups can be found: cultivated trees, wild trees, and their natural crosses. Numerous investigations have focused on the morphology of cultivated and wild sweet chestnut trees, but their interactions remain underexplored. Accordingly, the goals of this research were: (1) to determine the fruit characteristics of the three sweet chestnut genetic groups; (2) to determine the morphological variability of the leaves of each group; (3) to study if there are significant correlations between the morphological characteristics of the leaves and fruits; and (4) to assess whether the morphological diversity correlates with the genetic diversity determined in our previous research. To answer these questions, we collected samples of fruits and leaves from 144 genotyped trees in north-eastern Adriatic. In total, 10 leaf and 9 fruit morphological traits, along with 11 qualitative fruit traits, were analyzed. We found that cultivated trees had the largest fruits and the lowest diversity, while wild trees had the smallest fruits and the highest diversity. The group of natural crosses was characterized by larger leaves and intermediate fruit traits. Furthermore, significant correlations were identified between fruit and leaf morphometric traits. Overall, our results indicated that fruit morphology could be used as a distinguishing factor between the three groups, and that morphological differences coincide with genetic variability. These findings highlight the importance of diversity in local chestnut orchards, which can be valuable for the growers looking for specific agronomic traits for breeding purposes.