1 Cauline leaves bipinnatifid (or merely deeply pinnatifid); basal leaves sessile; [endemic to GA]; [section Dissecti]

1 Cauline leaves entire or toothed; basal leaves petioled; [collectively widespread].

  2 Corolla 35-55 mm long; calyx 7-16 mm long (in flower).

    3 Stems glaucous and glaucous; leaves glaucous and glabrous; corolla glabrous internally and externally; [section Coerulei]

    3 Stems hairy; leaves not glaucous, hairy or not; corolla glandular-puberulent externally and internally in the throat; [section Cristati]

      4 Corolla white to pink

      4 Corolla purple or violet

  2 Corolla 10-35 mm long; calyx 2.5-8 mm long (in flower).

        5 Inflorescence with many nodes; anther cells dehiscing by short proximal slits; [s. GA south to s. FL]

        5 Inflorescence with <10 nodes; anther cells dehiscing their entire length; [collectively widespread].

          6 Corolla weakly bilabiate, white, unlined, glandular-puberulent within; stem leaves abruptly reduced upwards

          6 Corolla strongly bilabiate, white or variously pinkish to purplish, lined (except P. hirsutus and P. tenuiflorus), glabrous or pubescent with non-glandular hairs within; stem leaves gradually reduced upwards.

             7 Mid and upper stem (but below the inflorescence) glabrous or with short eglandular hairs distributed in patches or lines; lower lobes of the corolla essentially equaling the upper lobes; corolla throat not strongly 2-ridged within, the tube conspicuously dilated into the throat; [Penstemon digitalis complex].

               8 Corolla 20-35 mm long.

                 9 Corollas purplish to lavender; sepals linear-lanceolate, straight and attenuate, 5-9 mm long at anthesis; anthers glabrous to papillose

                 9 Corollas white with purple lines; sepals ovate to ovate-lanceolate, acuminate, 4.5-6.5 mm long at anthesis; anthers with several to many hairs

               8 Corollas 15-23 mm long.

                   10 Sepals 1.5-3.5 (-4.0) mm long; corollas white; [approaching our area in s. IN and s. IL]

                   10 Sepals 3-6 mm long; corollas white or tinged with lavender.

                     11 Leaves mostly 2.5-4 cm wide; anthers bearded with long papillae

                     11 Leaves mostly 1.5-2.5 cm wide; anthers glabrous or papillose

             7 Mid and upper stem (but below the inflorescence) pubescent throughout, consisting of short eglandular hairs and sometimes also with an overstory of longer glandular hairs; lower lobes of the corolla projecting beyond the upper lobes; corolla throat strongly 2-ridged on its floor, the tube also slightly to moderately dilated into the throat.

                       12 Stem vestiture (mid and upper stem, but below the inflorescence) of short eglandular hairs only (or rarely also with a few glandular hairs in P. smallii).

                          13 Leaves 4-28 mm wide, 4-5× as long as wide

                          13 Leaves 15-60 mm wide, 2.5-4× as long as wide; [Penstemon smallii complex].

                            14 Corollas 28-35 mm long, lavender, violet, or purple; staminodes 15-18 mm long, densely bearded in the upper 13-15 mm; largest leaf blades mostly 30-60 mm wide

                            14 Corollas 10-16 mm long, pale lavender, pink, violet, or almost white; staminodes 7-9 mm long, densely bearded in the upper 4-5 mm; largest leaf blades mostly 10-40 mm wide.

                              15 Leaves mostly 30-40 mm wide; corolla pale-lavender to whitish, usually strongly lined with dark purple; sepals linear-attenuate; [plants of dry to mesic calcareous uplands, of ne. AL and se. TN]

                              15 Leaves mostly 10-30 mm wide; corolla lavender, pink, or violet, inconspicuously lined with reddish-purple; sepals ovate-lanceolate; [plants of wetlands, of MS, LA, and westwards]

                       12 Stem vestiture (mid and upper stem, but below the inflorescence) of a mixture of long glandular hairs and short eglandular hairs.

                                16 Corolla throats closed or nearly so (the lower lip arching upwards and pressing against the upper lip); corollas unlined or very obscurely lined (except strongly lined in P. australis).

                                  17 Corollas unlined; inflorescence branches spreading-ascending, obviously diverging from the vertical inflorescence axis; [Penstemon hirsutus complex].

                                    18 Corollas tinged with purplish-violet, the lobes often white; leaves sparsely pubescent to glabrate, the pubescence often mainly restricted to the veins

                                    18 Corollas creamy-white throughout; leaves moderately to densely hairy across the surface

                                       19 Leaves puberulent or retrorsely hairy; stem leaf blades 3-8× as long as wide

                                       19 Leaves moderately to densely glandular-woolly, especially along the major veins on the lower surface; stem leaf blades 6-20× as long as wide

                                16 Corolla throats open, not as described above (except sometimes nearly closed in P. australis); corollas lined, at least internally; [Penstemon canescens complex].

                                         20 Corollas 14-23 mm long.

                                           21 Cauline leaf pairs (6-)8-12; stems retrorsely hairy but only sometimes ± glandular-pubescent distally; [sw. IL south to se AR, westward]

                                           21 Cauline leaf pairs 4-8; stems retrorsely hairy AND consistently glandular pubescent or glandular-villous distally (also glandular-villous proximally in P. pallidus) ; [collectively widespread]

                                             22 Sepals 2-3.5 mm long, 1-1.5× as long as wide; corollas pale lavender (sometimes faded to white in herbarium specimens); inflorescences more open; cauline leaf margins finely and regularly toothed

                                             22 Sepals 3-5 mm long, 1.5-2.5× as long as wide; corollas creamy white, with violet lines; inflorescences more condensed; cauline leaf margins subentire or irregularly serrate or dentate

                                         20 Corollas 20-32 mm long.

                                               23 Inflorescence branches spreading-ascending, obviously diverging from the vertical inflorescence axis; sepals 3.2-4.5 mm long; corollas 20-30 mm long; corolla:calyx length ratio 7-9; cauline leaf pairs 3-7