Two European biennials have been reported as casuals along the Atlantic seaboard. C. temulum L. has 6-10 rays, lance-ovate bractlets, and oblong to ovate lf-segments. C. bulbosum L. has 10-20 rays, lance- linear bractlets, and lanceolate to linear lf-segments.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.