Rhodora 34: 25. 1932.
Herbs, perennial, with thick rootstock. Stems erect, unbranched, 70–100(–130) cm, glabrous. Leaves: petiole 0–2 mm; blade lance-oblong to oblanceolate-oblong, 50–100 × 13–30 mm, base attenuate to cuneate, margins entire, apex usually acute, sometimes obtuse to rounded, minutely apiculate, abaxial surface glabrate to sparsely pilose, adaxial surface glabrous; venation pinnate, midvein prominent. Cyathial arrangement: terminal pleiochasial branches 3–6, each unbranched or 1–2 times 2-branched, occasionally appearing pendent; pleiochasial bracts lance-ovate, shorter than distal leaves; dichasial bracts distinct, cordate-deltate to reniform, base subcordate, margins entire, apex rounded; axillary cymose branches 0–10. Cyathia: peduncle 0–1 mm. Involucre narrowly campanulate, 2.1–3 × 3–4.2 mm, glabrous; glands 5, elliptic to slightly reniform, 1–1.2 × 1.5–2.1 mm; horns absent. Staminate flowers 10–15. Pistillate flowers: ovary glabrous; styles 3–3.5 mm, 2-fid. Capsules globose, 4.5–5.2 × 6–6.8 mm, 3-lobed; cocci rounded, verrucose, sometimes minutely so, glabrous; columella 4–4.8 mm. Seeds mottled silver-brown, ovoid-globose, 3–4 × 2.5–3.5 mm, smooth; caruncle subconic, reniform, 0.8–1.1 × 1.4–1.6 mm.
Phenology: Flowering and fruiting spring–fall.
Habitat: Dry to moist forests and slopes, rock outcrops, swamps or seeps, especially over calcareous rocks.
Elevation: 50–1100 m.
Del., Md., N.J., N.C., Ohio, Pa., Va., W.Va.
Euphorbia purpurea is primarily an eastern Appalachian forest species, but it also occurs in Adams, Highland, and Pike counties in southern Ohio. It is listed as endangered by Maryland, New Jersey, Ohio, and Pennsylvania, and is in the Center for Plant Conservation's National Collection of Endangered Plants.