Hybanthus verticillatus (Ortega) Baill.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Species Description - A southwestern sp., closely approaches our range in e. Kans. and may be sought in Mo. It is smaller, seldom over 4 dm, with narrow, subsessile, alternate to casually opposite or even verticillate lvs mostly well under 1 cm wide, and with smaller fls, frs, and seeds.