This study assessed the biochemical composition, antioxidant capacity, mineral content, and morphological features of leaves from 22 hazelnut cultivars cultivated under uniform ecological conditions in Giresun (Turkiye) during the 2023.2024 growing seasons. Results revealed significant inter-cultivar differences for all parameters (p < .05). Manganese (coefficient of variation, CV = 61.33%) and petiole length (CV = 40.71%) displayed the highest variability, while total antioxidant capacity (TAC) was relatively consistent variability (CV = 15.89%). Cultivars such as gCetiner,h gOkay 28,h and gGiresun Melezih exhibited elevated TAC and phenolic content. Copper showed a strong predictive value for TAC (p . .01), and significant correlations were observed between K . Cu and Ca . Mg. Principal component analysis explained 83.86% of total variation, effectively separating cultivars based on biochemical and mineral traits. Heatmap analysis further distinguished groups with unique mineral accumulation profiles. The findings underscore the nutritional and functional potential of hazelnut leaves, highlighting their relevance for breeding strategies targeting bioactive-rich genotypes and for the development of functional food ingredients derived from leaf biomass. Specifically, cultivars such as gCetiner,h gOkay 28,h and gCavcavah show strong potential for use in antioxidantenriched product formulations and as parental lines in breeding programs focused on health-promoting traits.
