Much like P. pycnanthemoides; stem often with only short hairs; mature cal 3-4.5 mm, its lower teeth 1-2 mm, usually longer than the upper; nutlets 0.5-1.3 mm, smooth or with a few short hairs at the summit; 2n=38. Woods; Va. to s. Ill., s. to n. Fla.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.