This study investigated leaf phenotypic variation in oak species to better understand how different groups of oaks adapt to diverse environmental conditions. We examined the leaf phenotypic traits of six oak populations in two mixed forests with differing species compositions: Zijin Mountain in Jiangsu Province, composed of Quercus acutissima, Q. variabilis, and Q. fabri; and Youhua Village in Anhui Province, consisting of Q. acutissima, Q. chenii, and Q. fabri. The results indicated that species in the Cerris group (Q. acutissima, Q. chenii, Q. variabilis) exhibited stable leaf morphology and higher fluctuating asymmetry (FA), suggesting adaptation to stable environments. In contrast, Q. fabri from the Quercus group showed higher phenotypic plasticity and lower FA, indicating a strategy for adapting to dynamic environments. The study also explored the relationship between FA and phenotypic plasticity, revealing that while both traits are influenced by environmental stress, phenotypic plasticity allowed for more flexible responses to environmental change Additionally, our research highlighted the role of hybridization and genetic coadaptation in influencing developmental stability, with higher hybridization rates in Q. fabri leading to greater morphological variability. These findings underscore the importance of environmental factors, genetic variation, and hybridization in shaping the adaptive strategies and phenotypic traits of oak species, providing valuable insights into the complexities of adaptation and species identification.