Arctium lappa L.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Species Description - To 1.5 or even 3 m; lvs petiolate, the petioles mostly solid, progressively shorter upwards, the blade ovate or broader, cordate, to 5 × 3 dm, thinly tomentose beneath, subglabrous above; infl corymbiform, with long, glandular or glandular-hairy peduncles commonly 3–10 cm; heads large, the invol (2.5–)3–4 cm wide, generally equaling or surpassing the fls, glabrous or slightly glandular, and often with a few long cobwebby hairs; achenes 6–7 mm; 2n=32, 36. Native of Eurasia, sparingly established as a weed along roadsides and in waste places over most of the n. U.S. and adj. Can. Aug.–Oct.