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| 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 lined; inflorescence branches erect-ascending, nearly paralleling the inflorescence axes |
| ............ ............ ........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 erect-ascending, nearly paralleling the inflorescence axes; sepals 4-5.2 mm long; corollas 20-25 mm long; corolla:calyx length ratio 4-5; cauline leaf pairs 5–8 |
............ ............ ............ ........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 |