Habitat
Dry or moist woods, rare (Gleason & Conquist, 1991) (G & C); mountain glades and swampy woods (Strausbaugh and Core, 1977) (S & C); a unified hydrologic setting, primarily ground water influenced, headwater wetlands (seepage swamps, spring swamps); groundwater discharge maintains perennially saturated soil environment which is never (or rarely) inundated by flooding. Occurs most commonly in seepage swamps or spring seeps at the headwaters of streams of creeks (Rawinski and Cassin, 1986). This description typifies some of the habitats found in New Jersey (Snyder, 1986b), West Virginia, Pennsylvania (Bier pers. comm., T. Smith pers. comm.), Virginia, Massachusetts (Bartgis, pers. comm.) and North Carolina (Rawinski & Cassin, 1986). Such habitats are perennially saturated due to a continual discharge of groundwater (Knoop, 1990), but are never (or rarely) flooded (Rawinski & Cassin, 1986). Within such seepage swamps, associates include Polemonium vanbruntiae, Carex mitchelliana, C. leptalea, Chrysosplenium americanum, Glyceria striata, Cirsium muticum, Rhamnus alnifolia, Scirpus rubrotinctus, Triadenum walteri and Penthorum sedoides (Rawinski & Cassin, 1986). Occasionally, however E. purpurea is found in non-moist conditions, reflecting the fact that the species is not an obligate hydrophile (Knoop, 1990; Rawinski & Cassin, 1986). The original description of the species by Rafinesque listed the habitat as the glades of the Pennsylvania Allegheny Mountains (Fernald, 1932). Approximately 25% of the known sites are not in wetland habitats, but include such habitats as white oak forest formed over hornblend and open pastures underlain by limestone (Knoop, 1990; Rawinski & Cassin, 1986). On pastured sites cattle conspicuously avoid eating Euphorbia and the species consequently flourishes (Rawinski & Cassin, 1986). Darlington's spurge (Euphorbia darlingtonii) can tolerate a wide range of light conditions, ranging from full sunlight of pastures to shaded forest floors (Rawinski & Cassin, 1986). In Ohio, a single population of glade spurge occurs on a steep, north-facing slope in the shade of a massive outcropping of ??? dolomite (Knoop, 1990). This population occurs in a moist, dolomitic soil within a mixed hardwood forest (Ohio Heritage Program, 1987) and numbers roughly 75 individuals (Knoop, 1990). The soil, roughly 25-45 cm in thickness, is typically dry at the top of the rock outcropping and mesic near its base. The mixed decidous forest community is dominated by Quercus muhlenbergii, Fraxinus quadrangulata, Cenchrus occidentalis, Viburnum prunifolium, Quercus rubra and Hydrangea arborescens (Knoop, 1990). Herbaceous associates include Aquilegia canadensis, Thalictrum dioicum, Carex eburnea, Impatiens pallida and Phlox divericata. Two sub-populations of the single extant New Jersey occurrences are located in open, mucky seepage areas adjacent to a small stream running through a rich, wooded coastal swamp (Snyder, 1986a, 1986b). Associates include Sphenoholis pensylvanica, Carex mitchelliana, Caltha palustris, Chrysosplenium americanum, Viola conspersa and Cirsium muticum (Snyder, 1986b). In Virginia, E. purpurea is known from four sites, occurring on lower slopes and floodplains in scattered colonies and a single high-altitude site at the crest of Russell Beartown Mountain (Ogle, 1989). Associates at low-elevation sites include Polemonium reptans, Microstegium vineum, Roripa palustris, Elephantopus carolinianus, Ranunculus repens and R. arborvitis. Pennsylvania populations of E. purpurea occur in both the eastern and western portions of the state. A single extant western population occurs in a seepage swamp along an intermontane valley stream (Bier pers. comm.). These oblong wetlands run parallel with the stream with seepage water slowly running through them. Associates include Symplocarpus feotidus, Alnus spp., Impatiens spp., Lendera benzoin (Bier pers. comm.). Four extant populations occur in eastern Pennsylvania. One eastern population occurs on a serpentine barren at the base of a slope along an intermittent stream (T. Smith pers. comm.; Rawinski & Cassin, 1986). A York County population occurs in much soil at the edge of a seepage hillside. The site is dominated by Symplocarpus foetidus (90% cover) with an overstory of Acer rubrum (T. Smith pers. comm.). The other two sites are large seepage swamps with small streams running through them. Associates include Acer rubrum, Fraxinus spp. and Quercus spp. In Maryland, E. purpurea occurs typically in seepage wetlands (shrub swamps) over greenstone (Bartgis pers. comm.). Associates in such habitats include arrow-wood, Alnus spp., swamp-pink, climbing fern and skunk cabbage. At one site along the Piedmont/Coastal Plain border, E. purpurea occurs on a sandy deposit. This site may occur on the coastal plain, a situation unique in the state. Associates are similar to those over greenstone. At all sites, canopies are relatively open (Bartgis pers. comm.). In West Virginia, Darlington's spurge (Euphorbia darlingtonii) occurs in habitats varying from seepage swamps to high-elevation, dry, upland pastures over limestone to cirumneutral alluviam along high-elevation rivers (Bartgis pers. comm.). Seepage swamp associates include Alnus spp., Rhamnus alnifolia and Polemonium vanbruntinae. Upland pasture associates include Poa pratensis and other pasture plants. In this habitat, E. purpurea has been found in extremely large numbers (in excess of 10,000 individuals) at one site (Bartgis pers. comm.)and is often looked upon as a weed by farmers. Cattle apparently select for E. purpurea by eating other competing forbs and grasses and by refusing to eat the poor-tasting spurge. At such dry, high-elevation sites, plants appear to thrive due to the frequent presence of fog and rainfall. At one other site, E. purpurea occurs on alluvium along a high-elevation river with small canopy breaks, where past river action has formed small depressions. Ostrich fern is an associate at these sites.