Plants 3–25 dm.
Stems minutely glandular-puberulent, sometimes floccose distally.
Leaves basal 40–55 cm, blades 30–40 cm, surfaces abaxially appressed white-tomentose; cauline reduced distally; petioles often floccose, glandular-puberulent.
Heads short- or long-peduncled.
Involucres 1.5–2.5 mm in diameter.
Phyllaries floccose and cobwebby throughout.
Disc florets 30+; corollas 9–13 mm, purple or rarely white, minutely glandular.
Fruits 5–8 mm, light brown; pappi 1–3 mm.
2n=36.
Roadsides, disturbed areas. Flowering Jun–Oct. 0–1000 m. Lava, WV. Scattered in northern North America; Asia, Europe. Exotic.
as described under Arctium tomentosum
Plants to 250 cm. Basal leaves: petioles hollow or solid, 10-15 cm, glandular-hairy; blades 30-40 × 16-28 cm, coarsely dentate to subentire, abaxially white-tomentose, adaxially green, sparsely short-hairy. Heads usually in corymbiform clusters, long-pedunculate. Peduncles 1.5-12 cm. Involucres 15-25 mm diam., densely cobwebby (rarely glabrate). Phyllaries linear to linear-lanceolate, inner usually purplish, margins with minute spreading or reflexed glandular hairs. Florets 30+; corollas rose-purple, (occasionally white), 9-13 mm. limb minutely glandular. Cypselae light brown, 5-8 mm; pappus bristles 1-3 mm. 2n = 36.Flowering summer-early fall (Jul-Oct). Waste places, roadsides, fields, forest clearings; 0-1600 m; introduced; Alta., Man., N.B., Nfld. and Labr. (Nfld.), N.S., Ont., P.E.I., Que., Sask.; Colo., Conn., Maine, Mass., Minn., Mo., N.H., N.Dak., Ohio, S.Dak., Vt.; Eurasia.Arctium tomentosum has been reported from Illinois, Iowa, Maryland, New Jersey, Oregon, Pennsylvania, South Carolina, and Wisconsin; I have not seen specimens.The involucres of Arctium tomentosum are usually very densely cobwebby.Exceptional forms of A. tomentosum have nearly glabrous involucres. Forms of A. minus with especially cobwebby involucres have been misidentified as A. tomentosum; they lack the corymbiform capitulescence and glandular corollas of the latter.