Penstemon sect. Coerulei
Penstemon
beardtongue, penstemon
glabrous, sometimes scabrous, glaucous.
prostrate, erect, ascending, or decumbent, glabrous or variously hairy, sometimes also glandular.
basal and cauline, sometimes basal absent or reduced, opposite, leathery, glabrous, rarely scabrous, glaucous;
basal and proximal cauline petiolate, sometimes short-petiolate (P. immanifestus, P. lentus);
cauline sessile, sometimes short-petiolate, blade obovate, ovate, spatulate, trullate, oblanceolate, lanceolate, oblong, elliptic, linear, or orbiculate, margins entire.
deciduous in shrubby species, rarely persistent, basal and cauline, sometimes only cauline, rarely only basal, opposite, rarely whorled, alternate, or subalternate distally;
petiole present or absent;
blade leathery or not, margins entire or variously toothed (1-pinnatifid in P. dissectus), distal leaf blade not needlelike or scalelike.
continuous or interrupted, cylindric, sometimes secund, axis glabrous, rarely scabrous or glutinous, cymes 2 per node;
peduncles and pedicels ascending to erect.
terminal, thyrses, sometimes racemiform or paniculiform due to expansion or reduction of cymose lateral branches and/or number of verticillasters;
bracts present.
present, rarely absent;
bracteoles smaller than calyx lobes, not surrounding calyx of flowers they subtend.
calyx lobes: margins entire or erose, herbaceous or ± scarious, glabrous, rarely scabrous, glandular, glandular-pubescent, or glutinous;
corolla lavender to blue, violet, purple, or pink, rarely white or red, bilaterally symmetric, rarely nearly radially symmetric (P. cyathophorus), weakly, rarely strongly, bilabiate, not personate, tubular-funnelform, funnelform, or weakly ventricose, rarely tubular-salverform or weakly ampliate, glabrous externally, rarely obscurely glandular, glabrous or hairy internally abaxially, throat slightly to abruptly inflated, not constricted at orifice, rounded abaxially, rarely slightly 2-ridged;
stamens included to exserted, filaments glabrous, pollen sacs opposite, rarely divergent or parallel, navicular, rarely explanate (P. murrayanus), dehiscing completely, connective splitting, sides glabrous, sutures papillate, sometimes smooth;
staminode included to exserted, flattened distally, (0.2–)0.4–3 mm diam., tip recurved, rarely coiled or straight, distal 10–50(–70)% hairy, hairs to 2.5 mm, rarely glabrous;
style glabrous.
bisexual;
sepals 5, proximally connate, calyx essentially radially symmetric, short-campanulate, rarely short-tubular, lobes ± ovate, lanceolate, round, elliptic, oblong, obovate, oblanceolate, truncate, linear, or orbiculate;
corolla ± white, pink, red, blue, purple, lilac, violet, or crimson, rarely yellow or orange, bilaterally symmetric, rarely nearly radially symmetric, ± bilabiate or bilabiate and personate, rarely nearly regular, salverform, tubular, funnelform, ventricose, ampliate, ventricose-ampliate, tubular-funnelform, or tubular-salverform, tube base not spurred or gibbous, lobes 5, abaxial 3, adaxial 2;
stamens 4, proximally adnate to corolla, didynamous, filaments glabrous or glandular-puberulent proximally, rarely pubescent proximally and/or distally;
staminode 1, threadlike to straplike;
nectaries epistaminal;
ovary 2-locular, placentation axile;
stigma capitate.
capsules, dehiscence septicidal, not densely packed with white, membranous hairs.
glabrous.
brown or dark brown, angled, angled-elongate, or disciform, 1.8–5.4 mm.
(2–)5–40(–100+), tan, brown, or black, angled, rarely reniform, patelliform, disciform, rounded, or angled-elongate, wings absent, sometimes narrow.
Penstemon sect. Coerulei
Penstemon
Species 20 (20 in the flora).
D. D. Keck (1951) proposed the section name Anularius for sect. Coerulei, believing that the name of Pennell was invalid. N. H. Holmgren (1979b) concluded that the section names of Pennell are valid and that sect. Anularius Keck is invalid; the new combinations by Keck in that publication lacked descriptions.
Members of sect. Coerulei usually are recognized by their mostly glabrous, glaucous, and fleshy herbage, their blue or pink corollas that are glabrous, rarely obscurely glandular, externally, and their relatively broad and heavily bearded staminodes. Penstemon murrayanus has red corollas and glabrous staminodes. Members of sect. Coerulei mostly occur on well-drained, sandy soils. Molecular data (C. A. Wessinger et al. 2016) support the monophyly of the section.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Species ca. 280 (239 in the flora).
Penstemon is nearly endemic to North America, with three species that range south into Guatemala; it is the third largest genus in number of species in the flora area after Carex (Cyperaceae) and Astragalus (Fabaceae). Some species, especially in the western United States, have exceedingly narrow ranges.
Orthography of the genus name varied from the 1700s into the early 1900s and is summarized by F. S. Crosswhite (1965d).
Monographic studies of most parts of the genus were carried out by F. W. Pennell (1920b, 1921, 1935, 1940), D. D. Keck (1932, 1936b, 1937, 1937b, 1938, 1940b, 1945), Keck and A. Cronquist (1957), and F. S. Crosswhite (1965, 1965b, 1965c, 1966, 1967, 1967b, 1967c). Many western species were studied for floristic treatments in the Intermountain region (N. H. Holmgren 1984, 2017) and California (Holmgren 1993; M. Wetherwax and Holmgren 2017, http://ucjeps.berkeley.edu/eflora/eflora_display.php?tid=11396).
Penstemon shares morphological similarities with Chionophila, most notably an epistaminal nectary of glandular hairs. Both genera have a base chromosome number of × = 8. R. M. Straw (1966) hypothesized the genera to be sister taxa. Relationships among genera in Cheloneae remain equivocal (A. D. Wolfe et al. 1997, 2002, 2006; S. L. Datwyler and Wolfe 2004). Penstemon is distinguished from Chionophila by shorter calyx tubes (the calyx lobes usually distinct nearly to their bases), thyrsoid inflorescences, bracteoles in the inflorescences, and unwinged or, rarely, narrowly winged seeds.
The only broad molecular survey of Penstemon (A. D. Wolfe et al. 2006) found limited support for morphology-based infrageneric groups, and it lacked sufficient resolution to test the monophyly of large parts of the genus. C. A. Wessinger et al. (2016) obtained better species-level resolution in a study that focused on several sections of the genus. Both studies demonstrated that some groups are monophyletic or could be made so with minor adjustments and suggested that the infrageneric classification that draws heavily on floral characters may need extensive revision. A major overhaul of the infrageneric classification of Penstemon must await studies to resolve topological incongruencies between gene trees and to provide greater resolution within and among clades, issues likely due to hybridization and the recent, rapid radiation of the genus. Except for shifts of some species among subgenera or sections, a morphology-based classification with two subgenera and 16 sections is followed here.
Published chromosome counts exist for about half of the species in the flora area. Most Penstemon species counted are diploid (2n = 16); published tetraploid, hexaploid, octoploid, and dodecaploid counts exist for 24 species in sect. Penstemon, sect. Saccanthera, and sect. Spectabiles in the flora area. Most polyploids are assumed to be allopolyploids owing to the high incidence of hybridization; that hypothesis has not been tested.
Although the taxonomy of Penstemon traditionally places heavy emphasis on flower morphology, not all authors have used descriptive terms consistently. An overview of important diagnostic terms as applied in this treatment follows.
Basic corolla parts are the tube, throat, and limb (with abaxial and adaxial lobes). Some authors use the term tube to refer to the entire corolla proximal to the limb. In most species, the basal part of the corolla, proximal to the point of adnation of the staminode, is cylindric and narrower than the rest of the corolla; that part of the corolla is herein called the tube. In most species, the corolla expands near the point of adnation of the staminode to the corolla, forming the throat; the throat extends from tube to limb. Relative to the tube, the throat can be unexpanded with essentially parallel surfaces (corolla salverform), slightly expanded with nearly parallel sides (corolla tubular), expanded with straight and slightly diverging surfaces (corolla funnelform), inflated abaxially (corolla ventricose), inflated adaxially (corolla ampliate), or inflated abaxially and adaxially (corolla ventricose-ampliate). Most species have distinctly bilaterally symmetric corollas; some (for example, Penstemon centranthifolius, P. cyathophorus, P. eatonii, P. goodrichii) have corollas nearly radially symmetric. Corollas with the abaxial surface of the throat strongly uparched and closing or nearly closing the orifice are described as personate.
Nectar guides are present in corollas of most species, especially those presumably pollinated by hymenopterans. Members of subg. Dasanthera basically lack nectar guides; the two prominent ridges in the abaxial surface of the throat usually are lighter in color compared to the rest of the corolla. This condition also occurs in some species in sect. Saccanthera.
The taxonomy of Penstemon relies heavily on stamen morphology, which varies among species in size, orientation, vestiture, dehiscence, and shape. Differences among species within sections are often subtle. Characters should be determined from mature anthers that have dehisced and shed their pollen. Pollen sac length is the distance from the distal tip of the sac to its point of confluence with the opposite pollen sac (the connective). Orientation refers to the relative position of paired pollen sacs at dehiscence: parallel (sacs parallel to each other and basically parallel to the filament); divergent (distal tips spreading from each other and the filament); and opposite (distal tips essentially opposite each other and in line with the point of attachment of the filament).
Sutures of dehisced pollen sacs vary from smooth to papillose (with papillae mostly less than 0.1 mm) or denticulate (teeth 0.1+ mm). Vestiture of the sides of the anthers varies from absent to densely lanate, the hairs reaching 4 mm and obscuring the external surface in most members of subg. Dasanthera.
Dehiscence patterns usually are consistent within a species with few exceptions. Complete dehiscence occurs when both pollen sacs open entirely from their apices proximally to, and across, the connective. Complete dehiscence can result in anthers that remain more or less boat-shaped (navicular) or become essentially flat (explanate). Two basic patterns of incomplete dehiscence exist: the proximal portion of each pollen sac can remain indehiscent (pollen sacs dehiscent distally), sometimes with only the connective not splitting, or the distal portion of each sac can remain indehiscent (pollen sacs dehiscent proximally). Anthers of the former type typically have been described simply as dehiscing incompletely proximally; the pollen sacs can remain straight, sometimes they twist sigmoidally. Anthers that dehisce incompletely distally usually are described as saccate because of their pouchlike appearance.
The diversity of floral forms in Penstemon has stimulated great interest in the evolution of floral morphology (R. M. Straw 1955, 1956, 1956b; J. Walker-Larsen and L. D. Harder 2001; M. C. Castellanos et al. 2004, 2006), pollination ecology and pollination syndromes (Straw 1963; F. S. Crosswhite and C. D. Crosswhite 1966; R. Schmid 1976; H. R. Lawson et al. 1989; R. R. Clinebell and P. Bernhardt 1998; R. S. Lange and P. E. Scott 1999; V. J. Tepedino et al. 1999, 2006, 2007; J. D. Thomson et al. 2000; Paul Wilson et al. 2004), and reproductive biology (R. L. Nielson 1998; J. Chari and Wilson 2001; G. Dieringer and L. Cabrera R. 2002; J. L. Hawk and Tepedino 2007). Studies show that flower color is a good predictor of pollen vector (red or pink, salverform or tubular flowers pollinated by hummingbirds; purple, blue, or white, tubular, funnelform, or ventricose flowers pollinated by hymenopterans). Hummingbird pollination has evolved independently nearly a dozen times in Penstemon.
Penstemons are popular as ornamentals. Readers interested in growing penstemons should consult R. Nold (1999) or D. Lindgren and E. Wilde (2003). Nearly two-dozen species of Penstemon throughout North America were used by Native American tribes for drugs, food, fiber, dyes, and ceremonies (D. E. Moerman 1998).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Corollas red; staminodes glabrous; pollen sacs explanate. | P. murrayanus |
1. Corollas lavender to blue, violet, purple, or pink, rarely white; staminodes hairy; pollen sacs navicular. | → 2 |
2. Pollen sacs parallel or divergent; stamens: 2 or 4 prominently exserted; corollas without nectar guides. | → 3 |
3. Stamens: 4 exserted; pollen sacs 1.2–1.5 mm; corollas 11–14 mm. | P. cyathophorus |
3. Stamens: 2 exserted; pollen sacs 2–3 mm; corollas 17–24 mm. | P. harringtonii |
2. Pollen sacs opposite or divergent; stamens included or longer pair reaching orifice to slightly exserted; corollas usually with nectar guides. | → 4 |
4. Corollas 21–48 mm, ampliate, glabrous internally, throats abruptly inflated. | → 5 |
5. Corollas 35–48 mm; cauline leaf blades spatulate to orbiculate. | P. grandiflorus |
5. Corollas 21–28 mm; cauline leaf blades lanceolate to linear. | P. haydenii |
4. Corollas 10–25(–28) mm, tubular-funnelform, tubular-salverform, funnelform, or ventricose, white-villous internally abaxially or glabrous, throats not abruptly inflated. | → 6 |
6. Corollas tubular-salverform; thyrses interrupted. | P. fendleri |
6. Corollas tubular-funnelform, funnelform, or ventricose; thyrses continuous or interrupted. | → 7 |
7. Stems 3–10(–15) cm; cauline leaf pairs 1–3; thyrses 1–6 cm; verticillasters 1–5(or 6). | P. bracteatus |
7. Stems (4–)7–77(–82) cm; cauline leaf pairs 1–8(or 9); thyrses (2–)3–37(–57) cm; verticillasters (2 or)3–20(–35). | → 8 |
8. Thyrses secund. | → 9 |
9. Cauline leaves 2–4 pairs; staminodes 8–9 mm, distal 3–4 mm sparsely to densely villous, hairs yellowish, to 1 mm; Arizona, Colorado, New Mexico, Utah. | P. lentus |
9. Cauline leaves 4–6 pairs; staminodes 10–13 mm, distal 4–6 mm densely villous, hairs golden yellow, to 2 mm; Colorado, New Mexico, Wyoming. | P. secundiflorus |
8. Thyrses cylindric. | → 10 |
10. Staminodes 2–3 mm diam.; corollas with nectar guides, sparsely to moderately white-villous internally abaxially, rarely glabrous. | P. osterhoutii |
10. Staminodes (0.2–)0.4–2 mm diam.; corollas with or without nectar guides, glabrous or sparsely white-villous internally abaxially. | → 11 |
11. Corollas pink or white. | → 12 |
12. Corollas white. | P. lentus |
12. Corollas pink. | → 13 |
13. Leaves: basal usually reduced or absent; corollas glabrous internally; staminodes: distal 0.5–1.5 mm lanulose, hairs to 0.6 mm. | P. flowersii |
13. Leaves: basal not reduced; corollas sparsely white-hairy internally abaxially or glabrous; staminodes: distal 2–6 mm villous, hairs to 1 mm. | → 14 |
14. Cauline leaf apices acute to acuminate; corollas tubular-funnelform; calyx lobes ovate to lanceolate, 4–8 × 1–2.5 mm. | P. angustifolius |
14. Cauline leaf apices obtuse to acute; corollas funnelform to ventricose; calyx lobes ovate, 5–8(–12) × 2–3.5 mm. | P. immanifestus |
11. Corollas blue, pinkish blue, lavender-blue, lavender, violet, or purple, rarely some individuals with corollas pink. | → 15 |
15. Cauline leaf blades ovate to orbiculate; corollas with nectar guides, villous internally abaxially. | P. mucronatus |
15. Cauline leaf blades elliptic to ovate, obovate, lanceolate, oblanceolate, or linear; corollas with or without nectar guides, glabrous or villous internally abaxially. | → 16 |
16. Stems decumbent to ascending, (4–)7–18(–30) cm; thyrses continuous; proximal bracts oblanceolate to lanceolate; corollas (10–)12–15 mm; pollen sacs 0.7–0.8 mm. | P. arenicola |
16. Stems ascending to erect, (5–)9–60(–82) cm; thyrses interrupted or continuous; proximal bracts orbiculate to ovate, lanceolate, oblong, or linear; corollas 10–22 mm; pollen sacs 0.7–1.6 mm. | → 17 |
17. Proximal bracts orbiculate to ovate; corollas lavender to bluish lavender or pinkish blue, glabrous internally; capsules 12–18(–20) mm. | P. buckleyi |
17. Proximal bracts ovate to oblong, lanceolate, or linear, rarely orbiculate; corollas blue, pinkish blue, bluish lavender, violet, or purple, hairy internally abaxially or glabrous; capsules 7–15 mm. | → 18 |
18. Corollas obscurely glandular externally or glabrous; cauline leaves 1–3 pairs; thyrses 3–15 cm, continuous, sometimes interrupted. | P. carnosus |
18. Corollas glabrous externally; cauline leaves 2–8 pairs; thyrses (2–)5–30(–37) cm, continuous or interrupted. | → 19 |
19. Staminodes 1–2 mm diam., distal 6–8 mm villous, hairs to 2.5 mm. | P. pachyphyllus |
19. Staminodes (0.2–)0.5–1.5 mm diam., distal 1.5–7 mm pilose to villous, hairs to 1.5 mm. | → 20 |
20. Cauline leaf blades: apices obtuse to acute, sometimes rounded or mucronate; peduncles to 12–28 mm; corolla throats 5–8 mm diam. | → 21 |
21. Cymes 1–3(or 4)-flowered; cauline leaves sessile; seeds 3.5–5 mm. | P. lentus |
21. Cymes (1 or)2–6-flowered; cauline leaves short-petiolate or sessile; seeds 2–4 mm. | → 22 |
22. Corollas bluish lavender to lavender, 15–22 mm; peduncles to 12 mm; calyx lobes ovate, 5–8(–12) mm, apices acuminate; staminodes: distal 2–5 mm densely villous, hairs yellowish, brownish, or orangish, to 1 mm. | P. immanifestus |
22. Corollas blue to violet, sometimes lavender, 12–20 mm; peduncles to 26 mm; calyx lobes ovate to lanceolate, (2.5–)4–7 mm, apices acute to acuminate or caudate; staminodes: distal 4–8 mm densely villous, hairs yellow to golden yellow, to 2.5 mm. | P. pachyphyllus |
20. Cauline leaf blades: apices acute to acuminate, sometimes mucronate (P. nitidus); peduncles to 3–4 mm; corolla throats 4–6 mm diam. | → 23 |
23. Cymes 2–5-flowered, verticillasters (2–)4–10; corolla tubes 4–6 mm; stems glabrous. | P. nitidus |
23. Cymes (2–)4–8(–12)-flowered, verticillasters (3–)5–15(–26); corolla tubes 5–9 mm; stems glabrous or scabrous. | → 24 |
24. Staminodes: distal 1.5–3.5 mm densely pilose, hairs to 0.6 mm; calyx lobes lanceolate, (3.2–)4.5–10 × 1.2–3.2(–3.8) mm; pollen sacs 0.7–1.3(–1.5) mm; Idaho, Nevada, Oregon, Washington. | P. acuminatus |
24. Staminodes: distal 4–6 mm sparsely villous, hairs to 1 mm; calyx lobes ovate to lanceolate, 4–8 × 1–2.5 mm; pollen sacs (0.9–)1.1–1.5 mm; Arizona, Colorado, Kansas, Montana, Nebraska, New Mexico, North Dakota, Oklahoma, South Dakota, Utah, Wyoming. | P. angustifolius |
1. Staminodes included, length 1/3–3/4 times corolla throats; pollen sacs explanate, sides usually densely lanate (subexplanate and sides glabrous in P. personatus). | subg. Dasanthera |
1. Staminodes included to exserted, if included, length 3/4+ times corolla throats; pollen sacs navicular, navicular-sigmoid, saccate, or explanate, sides glabrous or hairy, if lanate, hairs not concealing surfaces, or if nearly concealing surfaces, pollen sacs not explanate. | subg. Penstemon |
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