Annuals, (15-)30-80+ cm (taproots fibrous-rooted). Herbage puberulent (hairs abundant, curly). Stems single. Leaves evenly distributed; petiolate; blades obovate to oblong, 3-7(-12) × 1-3(-4) cm, usually 1-2-pinnate, bases tapered, ultimate margins dentate (distal leaves similar, clasping, bractlike). Heads 12-24 in corymbiform arrays. Calyculi 0 or of 1-5+ linear to filiform bractlets. Phyllaries ± 13 (± 21), 4-7+ mm, tips greenish or minutely black. Ray florets 0 or 1-8+; corolla laminae usually 1-2+ mm (barely surpassing phyllaries). Cypselae hairy (especially on angles). 2n = 40. Flowering late spring-summer (northern areas of cool, climate); winter (southern areas). Mildly disturbed woodlands, open, sandy sites; 100-300 m; introduced; B.C., N.B., Nfld. and Labr. (Nfld.), N.S., P.E.I., Que.; Calif., La., Mass., Mich., N.J., Ohio, Oreg., Pa., Wash., Wis.; Eurasia. Senecio sylvaticus is a Eurasian weed that favors cool, wet climates. It is well established in coastal areas of the Pacific Coast and in parts of Newfoundland and Quebec; elsewhere in the flora, it appears to be sporadic.
Annual 1.5-8 dm from a ±evident taproot, leafy throughout, generally simple to the infl, sparsely or moderately pubescent with crisp loose hairs, or subglabrous; lvs all ±pinnatifid and irregularly toothed, 2-12 cm נ4-40 mm; heads several or many, the disk 3-7 mm wide; invol 5-7 mm, its principal bracts ca 13; bracteoles inconspicuous or wanting, not black-tipped; rays reduced and inconspicuous, less than 2 mm; pappus very copious, equaling or surpassing the disk- fls; achenes strigillose-canescent; 2n=40. A weed in disturbed soil and waste places; native of Europe, established here and there in the n. part of our range, especially in n. N. Engl. July-Sept.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.