Field Evaluation of Wild Oakleaf Hydrangea Populations Highlights Trait Networks for Breeding Selection

Oakleaf hydrangea ( Hydrangea quercifolia Bartr.) is a southeastern US native shrub valued for its ornamental traits but limited by a narrow, cultivated genetic base and susceptibility to leaf spot diseases. To expand breeding potential, we conducted a 3-year provenance test of 17 wild populations spanning the species’ latitudinal range, evaluating architectural traits, floral display, growth dynamics, and leaf spot severity. Populations differed significantly across all traits evaluated. Latitude of origin showed a strong influence on plant size, with southern populations consistently growing taller and wider than more northern populations. Growth increase was variable and environmentally sensitive, showing no consistent latitudinal trend. Leaf spot severity varied significantly among populations, but was not correlated with latitude, suggesting genotype-driven resistance that is context dependent. Floral traits were highly variable and independent of geographic origin, indicating a broad potential for ornamental selection. Trait correlation networks revealed modular organization and biologically meaningful linkages, including trade-offs between compactness and disease susceptibility. Comparative analysis with container-grown evaluations confirmed several populations as consistently combining moderate vegetative vigor, strong floral display, and low leaf spot severity. These findings highlight the value of multienvironment testing and trait–network analysis for identifying resilient, ornamental genotypes and to provide a robust framework for expanding the genetic base of cultivated oakleaf hydrangea.