Annuals, (10-)50-100(-150+) cm. Stems erect. Leaves: petioles 5-20(-30) mm; blades deltate or ovate to elliptic, trullate, or lanceolate, 30-100(-150+ × 8-45(-80) mm, margins ± toothed, faces ± scabrellous, gland-dotted. Heads in ± spiciform arrays. Peduncles 0-1 mm. Involucres ± hemispheric, 3-4(-5) mm. Phyllaries: outer 3-5 distinct, ± herbaceous. Paleae linear, 2-2.5 mm. Pistillate florets 3-5; corollas 0.5-1 mm. Functionally staminate florets 8-12+; corollas 2-2.5 mm. Cypselae 2-3 mm. 2n = 34. Flowering Jul-Nov. Disturbed sites, moist soils; 10-500 m; Ala., Ark., Colo., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., La., Maine, Mass., Mich., Miss., Mo., Nebr., N.Mex., N.C., N.Dak., Ohio, Okla., Pa., S.C., S.Dak., Tenn., Tex., Va., W.Va., Wis.; Mexico (Tamaulipas).
From Flora of Indiana (1940) by Charles C. Deam
Known only from Gibson and Posey Counties. I found it to be frequent to common in hard, clay soil in a field on the border of Pitcher's "Lake," along the roadside on the south side of Half Moon Pond, and along the roadside for a mile or more along the Wabash River in the vicinity of Bone Bank, Posey County.
Annual weed 0.5-2 m; stem glabrous below, strigose near the middle, commonly spreading-hirsute above; lvs chiefly opposite (only some of the reduced upper ones alternate), petiolate, lanceolate to broadly ovate, ±serrate, acuminate, 5-15 נ2-7 cm, scaberulous-strigose; infl of several or many spiciform branches, the heads practically sessile in the axils of reduced, ovate to lance- linear, conspicuously ciliate-margined lvs 5-20 mm; invol 2-3.5 mm, its bracts 3-5, subtending the achenes, sparsely long-hirsute, broad and ciliate distally; pistillate fls with tubular cor 1-1.5 mm tending to persist on the resinous-dotted achene, sometimes subtended by very slender and inconspicuous receptacular bracts; 2n=34. Waste ground, especially in moist soil; Ind. to N.D., s. to Miss. and N.M., and occasionally intr. eastward. Sept., Oct. (I. caudata; I. ciliata)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.