Herbs, annual, up to 60-90 cm tall. Root fibrous, 3-5 mm thick, with many rootlets. Stem single, many from base, 3-5 mm thick, smooth, usually glabrous, sometimes less pilose. Leaves alternate, sessile or subsessile; leaf blade elliptic, 5-7 × ca. 3 cm, green, base truncate-rounded, margin entire, apex obtuse, with small tip. Primary involucral leaves 2 or 3, green with white margin, elliptic, 3-4 × 1-2 cm, base attenuate, margin entire, apex rounded, primary rays 2 or 3, 1-4 cm, pubescent or subglabrous; secondary involucral leaves elliptic, 1-2 cm × 5-7(-9) mm, attenuate at base, subsessile, apex obtuse. Cyathia single from axils of involucral leaves or numerous clustered, peduncle 3-5 mm, densely pilose; involucre campanulate, 5-6 × ca. 4 mm, pubescent outside, 5 lobes, lobes triangular to rounded, apex acute to emarginate, pubescent inside; glands 4, rounded, appendages white, longer and wider than gland. Male flowers many, exserted from involucre; bracts linear. Female flower: pedicel 3-5 mm, exserted from cup; ovary densely pilose; styles free, persistent; stigma slightly 2-lobed. Capsule subglobose, ca. 5.5 × 5.5 mm, pilose; fruiting pedicel 3-7 mm. Seeds globose-terete, 3.5-4 × 2.8-3 mm, light yellow to gray-brown, with tuberose or inconspicuous enation; caruncle absent. Fl. and fr. Jun-Sep.

Euphorbia marginata is sometimes grown for the cut flower trade.

Escaped and naturalized. Anhui, Fujian, Guangdong, Guangxi, Guizhou, Hainan, Hubei, Hunan, Jiangsu, Jiangxi, Ningxia, Shandong, Sichuan, Taiwan, Yunnan, Zhejiang; also cultivated in N China [native to North America; naturalized in the Old World].