This is largely midwestern but Pennell (1935) and others have also mapped disjunct plants in more eastern regions, especially N.Y. and southern New England. Those eastern plants (like most other Penstemon spp. in New England) appear to be largely adventive, arriving in the late 1800s. The species was described in 1903, and Pennell (1935) listed only one coll. from Ky., by H. Garman from "Lexington" at KY-Agr., but this coll. has not been located; it might have been the white-flowered variant of calycosus. The earliest verified records from Ky. appear to be colls. in the 1960s from LIVI (MEM), TRIG (APSC) and nearby counties. In Ky., pallidus is verified mostly from the former Big Barrens region or nearby; further east; there are also a few records from the Knobs but none from the Bluegrass or Appalachian regions. However, there has been much confusion with brevisepalus (in eastern regions of the state) and some with tenuiflorus (in western regions), sometimes suggesting hybrid origin (brevisepalus x tenuiflorus). P. pallidus often occurs with or near tenuiflorus along roads in the Shawnee Hills and Pennyrhile Karst Plain, but it is concentratred on less xeric sites with more acid soils. P. pallidus can also be confused with the white-flowered variant of calycosus, unless pubescence patterns are examined with care. Unfortunately, published keys have been somewhat varied and inconsistent; see Pennell (1935), F, Cr, Clements et al. (1998), Estes (2012), W and FNA 17. Based on more detailed descriptions (especially F and Y), pallidus (along with the Ozarkian P. arkansanas Pennell) differs from brevisepalus and canescens as follows: leaves relatively "firm to coriaceous" (versus "membranaceous and herbaceous"), the cauline ones usually lanceolate to oblong or linear and 0.5-2 cm wide (versus ovate to oblong or lanceolate and 1.5-4.5 cm wide), usually entire or remotely denticulate (versus serrulate to dentate); hairs on stems and leaves relatively dense, soft (somewhat "velvety" or "velutinous") and short (mostly 0.1-0.5 mm versus often up to 0.5-1 mm); corollas white except for internal fine violet-purple lines (versus purple- or violet-tinged but often fading) and relatively small (ca. 16-23 mm long versus 15-30 mm). Sepals are intermediate in length: mostly 3-5 mm (versus 2-5.5+ mm).