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.
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.
