This species is doubtless adventive in our area. Along railroads and roadsides and in waste places. This plant much resembles the preceding [Euphorbia dentata] but can be separated from it by its alternate leaves, glabrous stem and leaves. The leaves of Euphorbia heterophylla vary from almost linear to fiddle-shaped.
Kearney and Peebles
Duration: Annual Nativity: Native Lifeform: Forb/Herb General: Simply branching, erect or ascending annual or perennial forb, stems not strigose. Leaves: Alternate between he first pair of secondary leaves and those at the stem tip, lanceolate to oblanceolate, 3-7 cm long, margins entire or serrulate, if toothed, the margins have 1-2 erect lobes. Flowers: Monoecious flowers borne in cup-shaped bracts (cyathia), clustered at branch tips, with yellow petaloid appendages. Leafy bracts just beneath the inflorescences turn a bright red. Fruits: Seeds 3-3.5 mm long. Ecology: Found in dry sites; 2,500-5,000 ft (762-1524 m); flowers August-October. Distribution: All of eastern US, from SD to NY, south to FL, west to CA; south to s MEX and in S. Amer.; Africa; Australia and Asia. Notes: There is some uncertainty with this taxa, Tropicos indicates it has an equally acceptable alternate name: Euphorbia heterophylla var. cyathophora. Leaf morphology is variable; some samples show leaves thin and blade-like, like a grass, and others thick with widely spaced teeth, somewhat like an oakleaf. Look to the bright red bracts to help identify this plant. 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. Synonyms: Euphorbia heterophylla var. cyathophora, many others, see Tropicos Editor: SBuckley 2010, FSCoburn 2015
Erect annual, to 1 m, usually branched, glabrous or nearly so (or the lvs seldom sparsely pilose beneath); lvs mainly or all alternate (or the uppermost opposite), variable, even on the same plant, from linear to broadly oblong or ovate or pandurate, entire or serrate to lobed, the upper mostly lobed and blotched with red or white at base; involucral gland solitary, bilabiate, cupulate, usually wider than high; fr smooth, 6-8 mm thick; seeds tuberculate, 3-3.5 mm, without a caruncle; 2n=28, 56. Moist soil, often in shade; trop. Amer. and s. U.S., cult. and escaped n. to Va., Wis., and Minn. Summer. (E. heterophylla and Poinsettia h., misapplied; Poinsettia c.)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.