Annuals or biennials, 10-140(-200) cm. Stem bases soft to hard, herbaceous, often hollow. Leaves: blades of mid cauline spatulate or oblong to obovate or lanceolate, 6-35 × 1-15 cm, bases auriculate, auricles deltate to lanceolate, ± straight, acute, margins usually pinnately (often runcinately) lobed, lobes ± deltate to lanceolate, not constricted at bases, terminals usually larger than laterals, entire or dentate. Peduncles usually glabrous, sometimes stipitate-glandular. Involucres 9-13+ mm. Phyllaries usually glabrous, sometimes tomentose and/or stipitate-glandular. Corollas: ligules ± equaling tubes. Cypselae dark brown, mostly oblanceoloid, 2.5-3.5+ mm, ribs 2-4 on each face, faces transversely rugulose or tuberculate across and between ribs; pappi 5-8 mm. 2n = 32, 36. Flowering (Apr-)Jul-Oct (year-round in south). Disturbed sites, gardens, roadsides, along streams; 0-2000 m; introduced; Greenland; St. Pierre and Miquelon; Alta., B.C., Man., N.B., Nfld. and Labr. (Nfld.), N.W.T., N.S., Ont., P.E.I., Que., Sask.; Ala., Alaska, Ariz., Ark., Calif., Colo., Conn., Del., D.C., Fla., Ga., Idaho, Ill., Ind., Iowa, Kansas, Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Mont., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.Dak., Ohio, Okla., Oreg., Pa., R.I., S.C., S.Dak., Tenn., Tex., Utah, Vt., Va., Wash., W.Va., Wis., Wyo.; Europe; introduced also in Mexico, West Indies, Bahamas, Central America, South America, Africa, Asia, Pacific Islands (New Zealand), Australia.
Annual 1-20 dm from a short taproot, glabrous except sometimes for a few spreading gland-tipped hairs on the invols and peduncles; lvs pinnatifid to occasionally merely toothed, soft, the margins only weakly or scarcely prickly, 6-30 × 1-15 cm, all but the lowermost ones prominently auriculate, the auricles well rounded but eventually sharply acute; lvs progressively less divided upward and Ā±reduced; heads several in a corymbiform infl, relatively small, 1.5-2.5 cm wide in fl; invol 9-13 mm in fr; fls 80-250 per head; cor-tube about equaling the ligule; achenes 2.5-3.5 mm, transversely rugulose and evidently to rather obscurely 3-5-ribbed on each face; 2n=32, 36. A cosmopolitan weed, native to Europe. July-Oct.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.