Annuals, (10-)20-50(-60+) cm (taprooted). Herbage glabrous or sparsely and unevenly tomentose when young. Stems usually 1. Leaves evenly distributed; petiolate; blades ovate to oblanceolate, 2-10 × 0.5-2(-4) cm, bases tapered, margins lobulate to dentate, ultimate margins often secondarily dentate to denticulate (distal leaves sessile). Heads 8-20 in loose, corymbiform arrays. Calyculi of 2-4(-6+) bractlets (prominent, black-tipped, lengths about ¹ / 4 phyllaries). Phyllaries ± 21, 4-6 mm, tips usually green, sometimes black. Ray florets 0. Cypselae usually sparsely hairy, sometimes nearly glabrous. 2n = 40. Flowering early spring (through summer in far North). Disturbed sites; 1-1000 m; probably introduced; Greenland; St. Pierre and Miquelon; Alta., B.C., Man., N.B., Nfld. and Labr., N.W.T., N.S., Nunavut, Ont., P.E.I., Que., Sask., Yukon; Ala., Alaska, Ariz., Calif., Colo., Conn., Del., D.C., Fla., Ga., Idaho, Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Mont., Nebr., Nev., N.H., N.J., N.C., N.Dak., Ohio, Okla., Oreg., Pa., R.I., S.C., S.Dak., Tenn., Tex., Utah, Vt., Va., Wash., W.Va., Wis., Wyo.; Eurasia. Senecio vulgaris has not been collected in the Canadian Arctic north of Hudson Bay.

A widely scattered weed of Eurasian origin, Senecio vulgaris is particularly abundant in southern areas of cool damp winters or northern areas of cool damp summers.

Plant: Annual 1-6 dm, arched upward, ± glabrous; stems generally 1-few per rosette Leaves: alternate; blades 2-10 cm (petiole weakly defined), oblanceolate to obovate, deeply and unevenly dentate to lobed INFLORESCENCE: primary inflorescence a head, each resembling a flower; heads discoid, 8-10; involucre cylindric to hemispheric; main phyllaries ± 21, 4-6 mm, tips often black; outer phyllaries 2-6, short, strongly black tipped Flowers: Ray flowers 0; Disk flowers < 40; corolla generally ± yellow; style tips truncate to obtuse, generally hair-tufted Fruit: achenes, subglabrous, cylindric; ribs shallow, often stiff-hairy; pappus of thin, minutely barbed deciduous bristles ± = fruit body Misc: Gardens, farmlands, other disturbed sites; < 1500 m.; Most of year