Range-wide phenotypic variation in seed and wing traits of Cyclocarya paliurus across environmental gradients in China

Cyclocarya paliurus is a wind-dispersed tree of high medicinal and economic value, yet range-wide variation in seed traits and its environmental correlates remain poorly quantified. We sampled 139 trees from 30 natural populations spanning the subtropical range in China and measured six traits (seed diameter, thickness, diameter-to-thickness ratio, wing diameter, volume, and thousand-kernel weight). Using a nested linear mixed framework, we partitioned variance within and among populations, calculated phenotypic differentiation (Vst), and related traits to geography and climate. Coefficients of variation ranged from 0.01–55.83%, with the highest mean CV for seed volume and the lowest for seed diameter. On average, 77% of the total variance was among populations (mean Vst ≈ 82%), indicating strong population differentiation. Altitude and thermal regime were the primary correlates of wing morphology and seed mass: populations at higher elevations and cooler sites tended to have larger wings and heavier seeds. PCA and k-means clustering resolved six geographically coherent phenotypic groups. Our results provide a quantitative baseline for climate-informed seed sourcing and conservation planning, and suggest that environmental filtering acts on coordinated suites of seed and wing traits rather than on single traits in isolation.