Much like no. 4 [Penstemon hirsutus (L.) Willd.]; stems usually solitary, glabrous below, finely puberulent in the infl; lvs entire to obscurely denticulate; cal 2-4 mm at anthesis, less than half as long as the fr; cor white throughout, evidently flaring in age. Dry calcareous soil; Ky. to Ala.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.