This is part of a rather poorly understood complex, together with P. kralii D. Estes and P. tenuis Small, that has been recently discovered in Tenn. and may be expected in Ky. (Ch+, Estes 2012 and pers. comm.). These species differ from the canescens complex and the hirsutus complex as follows (W): middle and upper stem below the inflorescence with only short eglandular hairs or rarely also with a few glandular hairs (versus with a mixture of long glandular hairs and short eglandular hairs ). P. smallii is a largely southern Appalachian endemic that is not verified in Ky. but it was reported by BA with no collection details, and it has also been reported from nearby on the Cumberland Plateau in Tenn. (K, Ch+), It is similar to canescens but differs in its generally larger flowers (FNA 17): corollas 28-35 mm long (versus ca. 10-30 mm); distal staminodes 13-15 mm long and more or less pilose (versus 4-12 mm long and distinctly hairy); proximal bracts 56-130 × 23-55 mm (versus 3-95 × 1-45 mm) with margins sharply serrate (versus entire to serrate). P. tenuis occurs on the Gulf Coastal Plain mostly west of the Mississippi Rv., but it has been found near the western border of Tenn. and in se. Mo. (Y); it may be expected in alluvial woodlands of far western Ky. P. tenuis is easily overlooked since it is superficially similar to laevigatus (sharing stems with short eglandular hairs) or perhaps alluviorum. It is usually more robust (with inflorescences up to 6-12 cm wide), and corollas are more pinkish- or reddish-purple, with somewhat unequal lobes as in the canescens complex, but not clearly flattened or strongly ridged (Pennell 1935, Y). Definitions of eastern Penstemon species, together with their evolutionary relationships, remain somewhat controversial. Few estimates of chromosome numbers have been made; these range from 2n = 16 in smallii, tenuis and pallidus, to 2n = 32 in tubaeflorus, to 2n = 96 in laevigatus, calycosus, deamii and digitalis (Broderick et al. 2011, Y, FNA 17).