With larger heads mostly 3-3.5 cm thick, is only casually intr. with us. It may reflect past hybridization of nos. 1 [Arctium minus Schkuhr] and 3 [Arctium lappa L.].

Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.

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