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.
Annual 1-4 dm from a ±evident taproot, leafy throughout, sparsely crisp-hairy or subglabrous; lvs coarsely and irregularly toothed to more often pinnatifid, 2-10 נ0.5-4.5 cm, the lower tapering to the petiole or petiolar base, the upper sessile and clasping; heads several or many, discoid, the fls all tubular and perfect; disk 5-10 mm wide; invol 5-8 mm, with ca 21 principal bracts and some short but well developed, black-tipped bracteoles; pappus very copious, from a little shorter than to equaling or generally surpassing the cors; achenes short-hairy chiefly along the angles; 2n=40. A weed in disturbed soil and waste places; native of the Old World, now widely distributed in n. temp. regions, and throughout our range. May-Oct.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.