Determining the degree of differentiation among individuals and populations is the foundation of species delineation. Morphological traits can provide good indication as to the variation that exists within and among species, but these traits can be flexible across growth environments, reflecting acclimation, rather than genetic differentiation. The southeastern azaleas present a complex problem in this respect because populations can show highly variable morphology (e.g., leaf shape), while at the same time, different species can have strongly similar traits. The geographic distributions of the southeastern azaleas show separation of species along temperature gradients, indicating a role for physiological temperature tolerance in speciation of this group. Here we report an analysis of morphological and physiological climate tolerance traits of specimens of R. prunifolium and R. cumberlandense grown in a common garden at the Auburn University Donald E. Davis Arboretum. We predict that R. cumberlandense and R. prunifolium will show significant differences in their physiological climate tolerance traits, with R. cumberlandense being adapted to colder, high-elevation environments compared to R. prunifolium.