Hydrangea quercifolia, oakleaf hydrangea, a flowering shrub native to woodlands of the southeastern United States. Oakleaf hydrangea has immense ornamental potential with four-season interest, including traits like showy panicles, striking foliage textures, red fall color, and exfoliating bark. Cultivars are often derived from wild selections either directly or only a few generations removed. Full genetic and phenotypic variation has not been evaluated for the species, and little is known about the diversity in horticulturally important traits for oakleaf hydrangea. For this study, growth and plant architecture of wild-collected oakleaf hydrangea seedlings were observed at the Otis L. Floyd Nursery Research Center in McMinnville Tennessee over a 3-year period. Seedlings from 14 populations of oakleaf hydrangea spanning the species’ native range were planted in a randomized complete block design containing six blocks and nine replications per block. Two-way ANOVA was used to partition variation in height, width, growth rate, and number of stems into sources attributable to block, population, and block × population. There were significant differences among populations for growth rate, size, and number of stems in all years. Southern populations were smaller than northern populations and showed a slower growth rate. Genetic and phenotypic variation shown among populations will guide conservation efforts and supplement breeding efforts for oakleaf hydrangea.
