Annuals, (10-)20-40(-60) cm (taprooted). Herbage densely fetid-viscid (hairs glandular). Stems single. Leaves evenly distributed; petiolate; blades obovate to oblong (pinnately dissected to pinnatifid), 2-7 × 1.5-4 cm, bases tapered or ± truncate, ultimate margins wavy or crenate-dentate (distal leaves sessile, smaller, ± clasping). Heads (1-)3-8(-30) in irregular, corymbiform arrays. Calyculi of 2-5 bractlets (largest to 4 mm). Phyllaries (± 13) ± 21, 5-7 mm, tips black. Ray florets ± 13; corolla laminae 1-2 mm (usually coiled, scarcely surpassing phyllaries). Cypselae usually glabrous, sometimes hairy. 2n = 40.
Flowering spring-fall. Disturbed sites, especially open sandy or gravelly places; 1-300 m; introduced; St. Pierre and Miquelon; Alta, B.C., Man., N.B., Nfld. and Labr. (Nfld.), N.S., Ont., P.E.I., Que., Sask.; Conn., Ill., Maine, Mass., Minn., N.H., N.J., N.Y., Pa., R.I., Wis.; Eurasia.
Senecio viscosus is a smelly, Eurasian weed now widely scattered in areas of cool damp climates, often as a casual waif. The viscid hairs trap wind-blown particles of sand, dust, and soot, which give the surfaces varying textures and colors.
Strong-scented annual 1-6 dm from a taproot, copiously and conspicuously glandular-hairy throughout; lvs equably distributed, pinnatifid and toothed, 3-12 נ1-5 cm, the lower petiolate; heads less crowded than in nos. 17 [Senecio sylvaticus L.] and 19 [Senecio vulgaris L.], the disk 7-15 mm wide; invol 6-8 mm, with ca 21 or seldom only 13 principal bracts and generally a few well developed but not black- tipped bracteoles; rays short but evident and loosely spreading in life, in herbarium specimens becoming rather circinate and inconspicuous, scarcely exceeding the pappus, which generally surpasses the disk- fls; achenes glabrous or nearly so; 2n=40. Native of Europe, now ±established as a weed in waste places from Que. and N.S. to Pa. and N.J., near the coast. July-Sept.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.