Oaks represent ecologically dominant and evolutionarily dynamic components of temperate forest ecosystems, yet intraspecific variation in reproductive traits remains insufficiently documented for many species. This study aimed to quantify and compare population-level variation in seed morphological and physical traits of Quercus cerris L. across different biogeographical regions of Türkiye. Mature seeds were collected from five natural populations located in the Black Sea (Samsun), Central Anatolia (Eskişehir), Aegean (Manisa and Afyonkarahisar), and Marmara (Balıkesir) regions. A total of 500 sound seeds were measured for seed length (SL), seed width (SW), seed shape (SS), seed size (SSi), seed volume (V), thousand-seed weight (TSW), and seed moisture content (SMC). Data were analyzed using one-way ANOVA, Duncan’s test, correlation analysis, hierarchical clustering, and principal component analysis (PCA). Significant differences among populations were detected for all investigated traits (p 0.05). Size- and weight-related variables exhibited the strongest inter-population differentiation, whereas SMC showed comparatively lower variation. PCA revealed that the first two principal components explained 98.19% of the total variance, with the primary axis associated mainly with seed size and mass. Western populations (Manisa and Balıkesir) were characterized by larger and heavier seeds, while other populations showed comparatively smaller morphometric values. These findings indicate pronounced intraspecific morphological differentiation in Q. cerris and suggest that seed size constitutes a key component of population-level variability. The results provide a scientific basis for seed source selection, conservation planning, and adaptive forest management under heterogeneous environmental conditions.
Bayrak et al. (Tue,) studied this question.