Plants 50-100(-200) cm. Leaves: basal blades ± elliptic, mostly 15-40 cm × 100-200+ mm (bases decurrent onto strongly ribbed petioles, margins callose-denticulate, otherwise entire, abaxial faces velvety-woolly, adaxial thinly hairy); cauline blades ovate or elliptic to lanceolate, 10-30 cm × 45-120 mm, bases cordate, clasping, margins serrate. Involucres (20-)30-40 mm diam. Outer phyllaries ovate, oblong, or ± deltate to lanceolate, 12-20(-25+) × 6-8(-20+) mm (abaxially velvety-hairy); inner phyllaries progressively narrower, less hairy, more scarious. Ray florets (15-)50-100+; corolla laminae (10-)20-30+ mm. Disc corollas 9-11 mm. Cypselae 3-4 mm, glabrous; pappi of (40-)50-60 basally connate, barbellate bristles or setiform scales 6-10 mm. 2n = 20.
Coarse perennial herb to 2 m, the stem finely spreading-hairy; lvs irregularly and shallowly dentate, densely velvety-woolly beneath, sparsely spreading-hairy or subglabrous above, the lower long-petiolate and elliptic, with blade to 5 נ2 dm, the upper becoming ovate, sessile and cordate-clasping; heads few, pedunculate, large, the disk 3-5 cm wide, the invol 2-2.5 cm; outer bracts broad, herbaceous, densely short-hairy; inner bracts narrow, subscarious, glabrous; rays numerous, slender, 1.5-2.5 cm; achenes glabrous, columnar and ±distinctly quadrangular, multistriate; pappus-bristles united at base, often in groups; 2n=20. Intr. from Europe; cult., escaped, and sparingly naturalized in moist or wet disturbed sites. May-Aug.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.