Euphorbia purpurea tends to occur in rich, cool woods along seeps, swamps or streamside, often influenced by circumneutral bedrock such as limestone or Ordovician sandstone (Fortney 1975). The species is primarily known from the interior highlands of Maryland, North Carolina, Ohio, Pennsylvania, and the Virginias, although a few populations persist in Delaware and New Jersey (Ogle 1989, NatureServe 2001). There, the growing season is short and precipitation amounts are high relative to the lower elevation regions (Fortney 1975). Other plant species observed in these areas include disjunct northern taxa like balsam fir (Abies balsamifera), glaucus willow (Salix sp.), Alder-leaved buckthorn (Rhamnus alnifolia), Nannyberry (Viburnum lentago), purple avens (Geum rivale) and highbush cranberry (Viburnum trilobum), trembling aspen, fire cherry, red raspberry, and swamp Saxifrage (Fortney 1975, 1993). Other associated species described from the single Ohio occurrence include bulblet fern (Cystopteris bulbifera), ginger (Asarum canadense), and goatsbeard (Aruncus dioicus), also indicative of rich soils. NOTE: Euphorbia purpurea is considered a facultative wetland plant (USDA 2001), but Gleason and Cronquist (1991) describe the habitat as dry or moist woods.