Reproductive Constraints in Camellia gauchowensis: Insights from Flowering Phenology, Pollen Traits and Pollinator Activity

Camellia gauchowensis is widely distributed in South China. Field observations indicate that it produces abundant flowers but yields relatively few fruits under natural conditions. Understanding the intrinsic and extrinsic drivers of this low fruit output is essential both for revealing adaptive strategies in oil-tea camellia and informing cultivation improvement. In this study, we comprehensively investigated the flowering phenology, floral traits, pollen traits, pollinator activity, and breeding-system characteristics of C. gauchowensis. The results showed that C. gauchowensis produces perfect flowers but suffers from a narrow effective pollination window during its late-autumn-to-winter flowering period. Stomium-cell contaminants mixed with pollen grains may contribute to its poor pollen germination capacity. Cytochemical staining (TTC and FDA) significantly overestimated viability compared to in vitro germination results, and thus could not serve as a reliable substitute for functional pollen assessment. Both the outcrossing index and the pollen–ovule ratio indicated that C. gauchowensis exhibits a reproductive tendency toward outcrossing, with its sexual reproduction largely dependent on pollinators. Among the recorded floral visitors, Apis cerana represents the most promising pollinator candidate owing to its numerical dominance, frequent stigma contact, and superior cold-tolerance capacity. Our results reveal that reproductive success in C. gauchowensis is collectively constrained by multiple factors: a narrow effective pollination window, low pollen viability, winter-driven pollinator scarcity, and its reproductive tendency toward outcrossing. This study elucidates the coupled intrinsic–extrinsic mechanisms underlying low fruit output in this winter-flowering oil-tea camellia and provides theoretical underpinnings for pollination management and high-yield cultivation of this economically important woody crop.