An allopolyploid (2n=36) with L. purpureum as one parent, is rarely adventive in the ne. part of our range. It differs from the latter in its irregularly incised-toothed lvs, the upper often ±decurrent onto the petiole.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.