Erect annual, 2-6 dm, often branched, with hairy herbage; lvs all or mostly opposite, petiolate, linear to ovate, coarsely toothed to subentire; infl congested, mingled with reduced green lvs; involucres 2-3 mm, with fimbriate lobes and a conspicuous, fleshy, flattened-obconic, tangentially bilabiate gland; styles bifid half their length, or deeper; fr smooth, 5 mm thick; seeds ovoid, rough-tuberculate, 2.5-3 mm, usually carunculate; 2n=14(?), 28, 56. Dry soil; Ill. and Wis. to Wyo. and Mex., and established as a weed on roadsides and waste places, especially in cindery soil, e to Mass., N.Y. and Va. July-Sept. (Poinsettia d.)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Duration: Annual Nativity: Non-Native Lifeform: Forb/Herb General: Simply branching, erect or ascending annual forb to 60 cm tall, stems strigose with gland-like stipules. Leaves: Mostly opposite, (lower ones sometimes alternate), lanceolate to oblanceolate, 3-7 cm long, margins entire or shallowly toothed. Flowers: Monoecious flowers borne in cup-shaped bracts (cyathia), clustered at branch tips, with white petaloid appendages. Fruits: Ovaries pubescent, capsules strigose, seeds not sharply quadrangular. Ecology: Found on dry plains and hills; 3,000-8,000 ft (914-2438 m); flowers August-October. Distribution: Most of eastern US, from IA to MA, south to GA, west to CA; south to s MEX, and in S. Amer.; also in Europe. Notes: Distinguished from other Euphorbia in our area by the combination of being erect annuals with opposite branching; unlobed, dentate leaves 4-8cm long that are clustered near the top of the plant, the cupped glands of the cyathia and strongly 3-lobed ovaries. Differentiated from the similar, introduced E. davidii by having rounded seeds, as opposed to angular in davidii; the hairs on the undersides of leaves are not strongly tapered, and non glandular appendages of the cyathium. This species has seeds which are not sharply quadrangular, which differentiates it from Euphorbia cuphosperma; E. cuphosperma formerly was considered a variety of Euphorbia dentata. Ethnobotany: Specific use of the species is unknown, but the genus was used as an infusion to treat diabetes, mouth, and skin sores, and as a bath to treat fevers, chickenpox, smallpox, and gonorrhea. In infusion of the roots was taken to invoke diarrhea. Etymology: Euphorbia is named for Euphorbus, Greek physician of Juba II, King of Mauretania, while dentata means toothed like a saw. Synonyms: None Editor: LCrumbacher 2011, FSCoburn 2015
From Flora of Indiana (1940) by Charles C. Deam
Along railroads and roadsides, in fallow fields, and rarely in open woodland. This species is no doubt adventive from the west. It was unknown to our earlier botanists. The leaves vary in width and a narrowleaf form has been named