This large colonial shrub occurs mostly in or near Appalachian regions of eastern states, and is restricted to acid soils. Disjunct western colls. from parks in CUMB (KY) and EDMO (DHL) may well be from cultivated plants but cannot be completely discounted. There is also an anomalous report from TAYL (Gm). The local dominance of this species in sandstone ravines tends to reduce diversity in ground vegetation (D. Dourson, pers comm.); past logging and lack of fire may be factors that have promoted it. R. maximum in the Blue Ridge also appears to have generally increased in abundance after the wave of industrial logging ca. 1900 to 1950, but there has been some recent local decline involving diseases that remain poorly understood (Baird et al. 2014, Brooks et al. 2019). Although the foliage is generally considered somewhat toxic to mammalian herbivores, deer will browse plants in winters with low mast production (Johnson et al. 1995).