Penstemon

From Wikipedia, the free encyclopedia

Penstemon
Penstemon palmeri closeup-400px.jpg
Penstemon palmeri
Scientific classification e
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Clade: Asterids
Order: Lamiales
Family: Plantaginaceae
Tribe: Cheloneae
Genus: Penstemon
Schmidel
Species

See text.

Penstemon /ˈpɛnstɪmən/,[1] the beardtongues, is a large genus of roughly 250 species of flowering plants native mostly to the Nearctic, but with a few species also found in the North American portion of the Neotropics. It is the largest genus of flowering plants endemic to North America.[2][3] Formerly placed in the family Scrophulariaceae by the Cronquist system, new genetic research has placed it in the vastly expanded family Plantaginaceae.[4][5]

A prominent, often hairy, staminode is the most distinctive feature of this genus, as in this Penstemon rupicola flower
Golden-beard Penstemon (Penstemon barbatus)
Penstemon bridgesii
Bellflower Beardtongue (Penstemon campanulatus)
Penstemon confertus
Talus Slope Penstemon (Penstemon digitalis)
Lowbush Penstemon (Penstemon fruticosus)
Davidson's Penstemon (Penstemon davidsonii)
Lilac Penstemon (Penstemon gracilis)
Hairy Beardtongue (Penstemon hirsutus)
Penstemon hirsutus pubescens
Pineneedle Beardtongue (Penstemon pinifolius)
Littleflower Penstemon (Penstemon procerus)
Serrulate Penstemon (Penstemon serrulatus)
Prairie-clover (Penstemon speciosus)

They have opposite leaves, partly tube-shaped, and two-lipped flowers and seed capsules. The most distinctive feature of the genus is the prominent staminode, an infertile stamen. The staminode takes a variety of forms in the different species; while typically a long straight filament extending to the mouth of the corolla, some are longer and extremely hairy, giving the general appearance of an open mouth with a fuzzy tongue protruding and inspiring the common name beardtongue.

Most penstemons are deciduous or semi-evergreen perennials, the remainder being shrubs or subshrubs. Heights can range from 10 cm to as much as 3 metres.

The one Asiatic species previously treated in Penstemon is now placed in a separate genus Pennellianthus. This leaves Penstemon a mostly Nearctic genus, with a few neotropical species. Although widespread across North America, and found in habitats ranging from open desert to moist forests, and up to the alpine zone, they are not typically common within their range.

History[]

John Mitchell published the first scientific description in 1748; although he only named it as Penstemon, we can identify it as P. laevigatus. Linnaeus then included it in his 1753 publication, as Chelone pentstemon, altering the spelling to better correspond to the notion that the name referred to the unusual fifth stamen (Greek "penta-", five). Mitchell's work was reprinted in 1769, continuing with his original spelling, and this was ultimately accepted as the official form, although Pentstemon continued in use into the 20th century.

Although several more species were found in the 18th century, they continued to be classified in Chelone until about the 1820s. The period of 1810 to 1850 increased the number of known species from 4 to 63, as expeditions traveled through Mexico and the western United States, followed by another 100 up to 1900.

During this time, seeds began to be offered for sale in Europe, the earliest known dating from 1813, with John Fraser offering four species in London, followed by Flanagan & Nutting offering nine species in their 1835 catalog. Subsequently many hybrids were developed in Europe.

Fieldwork in the remote parts of the Great Basin during the 20th century brought the total number of species known to over 250. The genus was extensively revised by David Keck between 1932 and 1957.

In 1946 the American Penstemon Society (link at bottom) was formed to promote both horticultural and botanical interest.

Uses[]

Some Native American tribes used penstemons as medicinal remedies for humans and animals.[6] Today its primary use is ornamental.

Horticulture[]

Although penstemons are among the most attractive native flowers of North America, Europe has traditionally been far more active in their hybridization with hundreds of hybrids developed since the early 19th century. The earliest development is somewhat shrouded in mystery; for instance Flanagan & Nutting's 1835 catalog mentions a 'Penstemon Hybridum' but does not describe it.

By 1860, a half-dozen French growers are known to have developed hybrids, most notably Victor Lemoine, while in 1857 the German Wilhelm Pfitzer listed 24 varieties. In 1861 the British Royal Horticultural Society held trials in which 78 varieties were entered. The Scottish firm of John Forbes first offered penstemons in 1870, eventually becoming the biggest grower in the world; in 1884 their catalog listed 180 varieties. By 1900 Forbes had offered 550 varieties, while Lemoine had developed nearly 470 by the time of his death in 1911. Few of these have survived to the present day.[citation needed]

A number of different species have been used in the hybridization process, notably and P. hartwegii.

In North America, penstemons are often used in xeriscape landscaping, as many are native to desert or alpine regions and thus quite hardy. One of the largest collections of penstemons in North America is found at The Arboretum at Flagstaff, Arizona, which hosts a Penstemon Festival each summer.[7]

Cultivars[]

The following species and cultivars have gained the Royal Horticultural Society's Award of Garden Merit:-[8]

  • 'Andenken an Friedrich Hahn'[9] (deep red)
  • 'Beech Park'[10] (pink/white)
  • 'Connie's Pink'[11] (rose pink)
  • 'Evelyn'[12] (rose pink)
  • 'George Home'[13] (red/white)
  • 'Hewell Pink Bedder'[14] (pink/white)
  • 'Hidcote Pink'[15]
  • 'Margery Fish'[16] (purple/blue)
  • 'Maurice Gibbs'[17] (purple-red/white)
  • 'Osprey'[18] (pink/white)
  • P. hartwegii[19] (scarlet)
  • P. isophyllus[20] (pale pink)
  • P. pinifolius 'Wisley Flame'[21] (orange-red)
  • P. rupicola[22] (pink)
  • 'Port Wine'[23] (deep red/white)
  • 'Raven'[24] (purple/white)
  • 'Rich Ruby'[25]
  • 'Roy Davidson'[26] (pink/white)
  • 'Rubicundus'[27] (red/white)
  • 'Schoenholzeri'[28] (red)
  • 'Sour Grapes'[29] (purple/blue)
  • 'Stapleford Gem'[30] (purple/blue)

Others include 'Dark Towers', developed by Dale Lindgren at the University of Nebraska.[31]

Species[]

  • Pennell – Firleaf beardtongue
  • Evert – Absaroka Range beardtongue
  • L.O. Williams – Stemless beardtongue
  • Penstemon acuminatus Dougl. ex Lindl. – Sharpleaf penstemon
  • Pennell & Nisbet – Los Alamos beardtongue
  • Greene – Alberta beardtongue
  • Nutt. – White penstemon
  • M. E. Jones
  • Penstemon albomarginatus M.E. Jones – White margin penstemon, whitemargin beardtongue, whitemargin penstemon
  • Penstemon alluviorum Pennell – lowland beardtongue
  • Torr. – bush penstemon, gilia beardtongue, gilia penstemon
  • N. Holmgren & L. Shultz – sandloving penstemon
  • Penstemon anguineus Eastw. – Siskiyou beardtongue
  • Penstemon angustifolius Nutt. ex Pursh – broad-beard beardtongue, broadbeard beardtongue, narrowleaf penstemon
  • Greene – Nevada sanddune beardtongue, sanddune penstemon
  • A. Nels. – sand penstemon
  • Rydb. – stiffleaf penstemon
  • Penstemon arkansanus Pennell – Arkansas beardtongue
  • Penstemon attenuatus Dougl. ex Lindl. – sulphur penstemon
  • Welsh – Kaiparowits beardtongue
  • Pennell – Colorado beardtongue
  • Small – Eustis Lake beardtongue
  • Penstemon azureus Benth. – azure penstemon
  • Hook. – baccharisleaf beardtongue [32]
  • Penstemon barbatus (Cav.) Roth – Golden-beard Penstemon or Beardlip penstemon
  • Penstemon barnebyi N. Holmgren – Barneby's penstemon, White River Valley beardtongue
  • Penstemon barrettiae Gray – Barrett's beardtongue
  • Penstemon bicolor (Brandeg.) Clokey & Keck – pinto beardtongue, pinto penstemon
  • Keck – Red Canyon beardtongue
  • (Keck) Nisbet & R.C. Jackson – shortstem beardtongue, shortstem penstemon
  • Penstemon brevisepalus Pennell – short-sepaled beardtongue
  • Keck – Bryant's beardtongue
  • Pennell – buckley penstemon, Buckley's beardtongue
  • Penstemon caesius Gray – San Bernardino beardtongue
  • Nutt. ex Gray – mat penstemon
  • Penstemon calcareus Brandeg. – limestone beardtongue
  • Penstemon californicus (Munz & Johnston) Keck – California penstemon
  • Penstemon calycosus Small – longsepal beardtongue
  • (Cav.) Willd. – bellflower beardtongue
  • Penstemon canescens (Britt.) Britt. – eastern gray beardtongue
  • Woot. & Standl. – cardinal beardtongue
  • T.J. Howell – Cardwell's beardtongue
  • Pennell – fleshy beardtongue
  • Pennell – Cary's beardtongue
  • Penstemon centranthifolius Benth. – scarlet bugler
  • Penstemon cinicola Keck – ash penstemon
  • Gray
  • Penstemon clevelandii Gray – Cleveland's beardtongue
  • Penstemon clutei A. Nels. – Sunset Crater beardtongue, Sunset Crater penstemon
  • Penstemon cobaea Nutt. – cobaea beardtongue, Cobaea penstemon
  • Penstemon comarrhenus Gray – dusty beardtongue, dusty penstemon
  • (Keck) Crosswhite – compact penstemon
  • Keck – Tunnel Springs beardtongue, Tunnel Springs penstemon
  • Dougl. ex Lindl. – yellow penstemon
  • M.E. Jones – Owens Valley beardtongue, Owens Valley penstemon
  • A. Nels. – Crandall's beardtongue
  • A. Nels. (pro sp.) – Crider penstemon, Crider's penstemon
  • Gray – Cusick's beardtongue
  • Hook. – Wasatch beardtongue
  • Penstemon cyaneus Pennell – blue penstemon
  • Penstemon cyanocaulis Payson – bluestem beardtongue
  • Rydb. – Northpark penstemon, sagebrush beardtongue
  • Gray – Cochise beardtongue, purple penstemon
  • Penstemon davidsonii Greene – Davidson's penstemon, timberline penstemon
    • Penstemon davidsonii var. davidsonii – Davidson's penstemon
    • Penstemon davidsonii var. menziesii – Menzies' penstemon
    • Penstemon davidsonii var. praeteritus – timberline penstemon
  • Pennell – Deam's beardtongue
  • Crosswhite – Mt. Graham beardtongue
  • Penstemon debilis O'Kane & J. Anderson – Parachute beardtongue
  • Penstemon degeneri Crosswhite – Degener's beardtongue
  • Penstemon deustus Dougl. ex Lindl. – scabland penstemon
  • Penstemon digitalis Nutt. ex Sims – talus slope penstemon, foxglove beardtongue
  • Rydb. – twoleaf beardtongue
  • Keck – Catalina beardtongue
  • Ell. – dissected beardtongue
  • N. Holmgren – Mt. Tumbull beardtongue
  • M.E. Jones ex Pennell – Jones's penstemon, Jones' beardtongue
  • A. Davids. (pro sp.) – dubius penstemon
  • Penstemon eatonii Gray – Eaton penstemon, Eaton's penstemon, firecracker penstemon
  • Pennell – rockvine penstemon
  • Coult. & Fisher – rocky ledge penstemon
  • Penstemon eriantherus Pursh – fuzzytongue penstemon
  • English – glaucous beardtongue
  • Keck – unusual beardtongue
  • Torr. & Gray – fendler penstemon, Fendler's beardtongue, Fendler's penstemon
  • Penstemon filiformis (Keck) – Keck threadleaf beardtongue
  • Pennell – high mountain penstemon
  • D. Danley – Cordillia's beardtongue, Cordillia's penstemon
  • Penstemon floridus Brandeg. – Panamint beardtongue, Panamint penstemon
  • Neese & Welsh – Flowers' beardtongue
  • Penstemon franklinii Welsh – Franklin's penstemon
  • Torr. & Gray ex Gray – Fremont penstemon, Fremont's beardtongue
  • Penstemon fruticiformis Coville – Death Valley beardtongue, Death Valley penstemon
  • Penstemon fruticosus (Pursh) – Greene bush penstemon
  • Hook. – Gairdner's beardtongue
  • Penstemon gibbensii Dorn – Gibbens' beardtongue
  • Pursh – sawsepal penstemon, western smooth beardtongue
  • Dougl. – stickystem penstemon
  • Pennell – blueleaf beardtongue
  • (Piper) Pennell & Keck – globe penstemon
  • N. Holmgren – Lapoint beardtongue
  • Greene – Gorman's beardtongue
  • Penstemon gracilentus Gray – slender penstemon
  • Nutt. – lilac penstemon, slender penstemon
  • Penstemon grahamii Keck – Uinta Basin beardtongue
  • Penstemon grandiflorus Nutt. – large beardtongue, largeflowered penstemon
  • A. Nels. – Griffin's beardtongue
  • Penstemon grinnellii Eastw. – Grinnell's beardtongue
  • Heller – Guadalupe beardtongue
  • Gray – Hall's beardtongue
  • Gray – Harbour's beardtongue
  • Penl.
  • Penl. – Harrington's beardtongue
  • Penstemon hartwegii Benth. – Hartweg's beardtongue
  • Gray
  • Gray – Big Bend beardtongue
  • Penstemon haydenii S. Wats. – blowout beardtongue, blowout penstemon
  • Penstemon heterodoxus Gray – Sierra beardtongue, Sierra penstemon
  • Penstemon heterophyllus Lindl. – bunchleaf penstemon
  • Penstemon hirsutus (L.) Willd. – hairy beardtongue
  • Penstemon humilis Nutt. ex Gray – low beardtongue, low penstemon
  • Atwood & Welsh – Idaho beardtongue
  • N. Holmgren – Steptoe Valley beardtongue, Steptoe Valley penstemon
  • Penstemon incertus Brandeg. – Mojave beardtongue
  • Crosswhite – inflated beardtongue
  • Benth. – James penstemon, James' beardtongue
  • Penstemon janishiae N. Holmgren – Antelope Valley beardtongue, Janish's penstemon
  • Pennell
  • Pennell (pro sp.) – Jones' penstemon
  • S. Wats. – King's beardtongue, King's penstemon
  • Penstemon labrosus (Gray) Hook. f. – San Gabriel beardtongue
  • Penstemon laetus Gray – mountain blue penstemon
  • Penstemon laevigatus Ait. – eastern smooth beardtongue
  • Pennell – southwestern beardtongue, southwestern penstemon
  • Hook. & Arn. – larchleaf beardtongue
  • Pennell – nodding beardtongue
  • A. Nels. – tufted penstemon
  • Pennell – smoothleaf beardtongue, smoothleaf penstemon
  • (Keck) Keck & Cronq. – Lemhi penstemon
  • Pennell – handsome beardtongue, handsome penstemon
  • Rydb. – Leonard's beardtongue, Leonard's penstemon
  • Pennell – Sevier Plateau beardtongue
  • Penstemon linarioides Gray – creeping penstemon, toadflax penstemon
  • (Pennell) S.L. Clark – longflower penstemon
  • (Gray) Gray – Lyall's beardtongue
  • (Keck) N. Holmgren – Marcus' beardtongue
  • Pennell – tiger beardtongue
  • Penstemon metcalfei – Metcalfe's beardtongue
  • A. Nels. (pro sp.) – bush penstemon, penstemon
  • Gray – Malheur penstemon
  • Eastw. – Moffatt's beardtongue
  • Penstemon monoensis Heller – Mono penstemon
  • Greene – cordroot beardtongue
  • N. Holmgren – Mount Moriah penstemon, Mt. Moriah beardtongue
  • Penstemon multiflorus Chapman ex Benth. – manyflower beardtongue
  • N. Holmgr.
  • Penstemon murrayanus Hook. – scarlet beardtongue
  • Keck – dwarf beardtongue
  • Penstemon navajoa N. Holmgren – Navajo Mountain beardtongue
  • Woot. & Standl. – New Mexico beardtongue
  • Penstemon neotericus Keck – Plumas County beardtongue
Penstemon newberryi, Yosemite National Park, 2005
  • Penstemon newberryi Gray – mountain pride, pride-of-the-mountains
  • Dougl. ex Benth. – waxleaf penstemon
  • Gray – Flagstaff beardtongue
  • Pennell – Oklahoma beardtongue, Oklahoma penstemon
  • Woot. & Standl. – Apache beardtongue
  • Pennell – Arizona beardtongue, coiled anther penstemon
  • Penstemon osterhoutii Pennell – Osterhout's beardtongue
  • Dougl. ex Hook. – eggleaf beardtongue
  • Penstemon pachyphyllus Gray ex Rydb. – thickleaf beardtongue, thickleaf penstemon
  • Penstemon pahutensis N. Holmgren – Pahute penstemon, Paiute beardtongue
  • Penstemon pallidus Small – pale beardtongue
  • Penstemon palmeri Gray – Palmer's penstemon, Palmer penstemon
  • Penstemon papillatus J.T. Howell – Inyo beardtongue
  • Gray (pro sp.) – Parish's penstemon
  • Penstemon parryi (Gray) – Gray Parry penstemon, Parry's beardtongue
  • Pennell – Montezuma County beardtongue
  • Pennell – Aquarius Plateau beardtongue
  • Penstemon patens (M.E. Jones) N. Holmgren – Lone Pine beardtongue, Lone Pine penstemon
  • A. Nels. & J.F. Macbr. – Payette beardtongue
  • Keck – Payson's beardtongue
  • Pennell – Peck's beardtongue
  • Munz & I.M. Johnston (pro sp.) – Peirson's penstemon
  • Penstemon penlandii W.A. Weber – penland beardtongue, Penland's beardtongue
  • Penstemon pennellianus Keck – Blue Mountain beardtongue
  • A. Nels. – Minidoka beardtongue
  • Penstemon personatus Keck – closethroat beardtongue
  • Brandeg. – lime penstemon, petiolate beardtongue
  • Penstemon pinifolius Greene – pineneedle beardtongue, pineneedle penstemon
  • Penstemon pinorum L.& J. Shultz – Pine Valley penstemon
  • Rydb. – broadleaf beardtongue, broadleaf penstemon
  • Greene western – whiteflower beardtongue, western whiteflower penstemon
  • Penstemon procerus Dougl. ex Graham – littleflower penstemon, pincushion beardtongue
  • Dougl. ex Lindl. – Chilean beardtongue
  • Crosswhite – Mt. Washington beardtongue, San Mateo penstemon
  • (Crosswhite) N. Holmgren – Kaibab Plateau beardtongue
  • Penstemon pseudospectabilis M.E. Jones – desert penstemon
  • Penstemon pudicus Reveal & Beatley – bashful penstemon, Kawich Range beardtongue
  • Nutt. – Salmon River beardtongue
  • Penstemon purpusii Brandeg. – Snow Mountain beardtongue
  • A. Nels. – Black River beardtongue
  • A. Nels. – matroot penstemon
  • Crosswhite – lanceleaf beardtongue, lanceleaf penstemon
  • Gray – Rattan's beardtongue
  • Payson ex Pennell – Adobe Hills beardtongue
  • Payson ex Pennell
  • Penstemon rhizomatosus N. Holmgren
  • Dougl. ex Lindl. – cutleaf beardtongue
  • Penstemon roezlii Regel – Roezl's penstemon
  • Penstemon rostriflorus Kellogg – beaked beardtongue, beakflower penstemon, Bridge penstemon
  • Keck – Wassuck penstemon, Wassuk Range beardtongue
  • Penstemon rupicola (Piper) T.J. Howell – cliff beardtongue
  • Penstemon rydbergii A. Nels. – meadow beardtongue, Rydberg penstemon, Rydberg's penstemon
  • Pennell – upland beardtongue
  • Penstemon scapoides Keck – pinyon beardtongue
  • Penstemon scariosus Pennell – White River beardtongue
  • Benth. – sidebells penstemon
  • (A. Nels.) Keck – shortlobe penstemon
  • A. Nels. – littlecup beardtongue
  • Penstemon serrulatus Menzies ex Sm. – serrulate penstemon
  • Heller – Small's beardtongue
  • Pennell – Wallowa beardtongue
  • Penstemon speciosus Dougl. ex Lindl. – prairie-clover, royal penstemon
  • Penstemon spectabilis Thurb. ex Gray – showy penstemon
  • (Gray) T.J. Howell – Sonoran beardtongue
  • Penstemon stephensii Brandeg. – Stephens' penstemon
  • Rydb. – Mancos penstemon, stiff penstemon
  • Penstemon strictus Benth. – Rocky Mountain beardtongue, Rocky Mountain penstemon
  • Rydb. – smooth penstemon
  • Pennell – finetooth beardtongue
  • M.E. Jones – hackberry beardtongue
  • Penstemon sudans M.E. Jones – Susanville beardtongue, Susanville penstemon
  • A. Nels. – superb beardtongue
  • Penstemon tenuiflorus Pennell – eastern whiteflower beardtongue
  • Penstemon tenuis Small – sharpsepal beardtongue
  • Greene – germander beardtongue
  • Penstemon thompsoniae (Gray) Rydb. – Thompson's penstemon, Thompson's beardtongue, Thompson penstemon
  • Penstemon thurberi Torr. – Thurber's penstemon, Thurber penstemon
  • Pennell – Tidestrom's beardtongue
  • N. Holmgren – Tiehm's beardtongue
  • Penstemon tracyi Keck – Trinity penstemon
  • Penstemon triflorus Heller – Heller's beardtongue
  • Dougl. ex Lindl. – Riggin's penstemon
  • Penstemon tubaeflorus Nutt. – white wand beardtongue
  • N. Holmgren – Tushar Range beardtongue
  • Pennell – Uinta Mountain beardtongue
  • Rydb. – oneside penstemon
  • Penstemon utahensis Eastw. – Utah penstemon
  • Penstemon venustus Dougl. ex Lindl. – Venus penstemon
  • Pennell ex Rydb. – Front Range beardtongue
  • Gray – upright blue beardtongue
  • Gray – Ward's beardtongue
  • Keck – Washington beardtongue
  • Gray – Watson's penstemon, Watson's beardtongue, Watson penstemon
  • B.L.Turner[33]
  • Gray – dark beardtongue, Whipple's penstemon
  • Rydb. – Wilcox's penstemon
  • Hook. – Wright's beardtongue
  • Penl. – Yampa beardtongue

See also[]

References[]

Notations[]

  • Way, D. and P. James. The Gardener's Guide to Growing Penstemons. David & Charles Publishers. 1998. ISBN 0-7153-0550-6

Footnotes[]

  1. ^ Sunset Western Garden Book, 1995:606–607
  2. ^ Jepson, Willis Linn; Holmgren, Noel H. (1993) [1925]. Hickman, James C. (ed.). The Jepson Manual: Higher Plants of California (First ed.). Berkeley, California: University of California Press. p. 1050. ISBN 0-52008255-9.
  3. ^ Wetherwax, Margriet; Holmgren, Noel H. (2012). Baldwin, Bruce G.; Goldman, Douglas; Keil, David J.; Patterson, Robert; Rosatti, Thomas J.; Wilken, Dieter (eds.). The Jepson Manual, Vascular Plants of California, Thoroughly Revised and Expanded (Second ed.). Berkeley, California: University of California Press. p. 1017. ISBN 9780520253124.
  4. ^ Olmstead, Richard G.; de Pamphilis, Claude W.; Wolfe, Andrea D.; Young, Nelson D.; Elisons, Wayne J.; Reeves, Patrick A. (February 2001). "Disintegration of the Scrophulariaceae". American Journal of Botany. 88 (2): 348–361. doi:10.2307/2657024. JSTOR 2657024. PMID 11222255.
  5. ^ Oxelman, Bengt; Kornhall, Per; Olmstead, Richard G.; Bremer, Birgitta (May 2005). "Further disintegration of Scrophulariaceae". Taxon. 54 (2): 411–425. doi:10.2307/25065369. ISSN 0040-0262. JSTOR 25065369.
  6. ^ Escamilla, G., et al. Penstemon ambiguus. Medicinal Plants of the Southwest. New Mexico State University. 2001. Updated 2008.
  7. ^ "Penstemon Festival". Thearb.org. Retrieved 2012-08-04.
  8. ^ "AGM Plants - Ornamental" (PDF). Royal Horticultural Society. July 2017. p. 75. Retrieved 2018-04-22.
  9. ^ "RHS Plant Selector Penstemon 'Andenken an Friedrich Hahn' AGM / RHS Gardening". Apps.rhs.org.uk. Retrieved 2021-01-27.
  10. ^ "RHS Plant Selector Penstemon 'Beech Park' AGM / RHS Gardening". Apps.rhs.org.uk. Retrieved 2021-01-27.
  11. ^ "RHS Plant Selector Penstemon 'Connie's Pink' AGM / RHS Gardening". Apps.rhs.org.uk. Retrieved 2021-01-27.
  12. ^ "RHS Plant Selector Penstemon 'Evelyn' AGM / RHS Gardening". Apps.rhs.org.uk. Retrieved 2021-01-27.
  13. ^ "RHS Plant Selector Penstemon 'George Home' AGM / RHS Gardening". Apps.rhs.org.uk. Retrieved 2021-01-27.
  14. ^ "RHS Plant Selector Penstemon 'Hewell Pink Bedder' AGM / RHS Gardening". Apps.rhs.org.uk. Retrieved 2021-01-27.
  15. ^ "RHS Plant Selector Penstemon 'Hidcote Pink' AGM / RHS Gardening". Apps.rhs.org.uk. Retrieved 2021-01-27.
  16. ^ "RHS Plant Selector Penstemon 'Margery Fish' AGM / RHS Gardening". Apps.rhs.org.uk. Retrieved 2021-01-27.
  17. ^ "RHS Plant Selector Penstemon 'Maurice Gibbs' AGM / RHS Gardening". Apps.rhs.org.uk. Retrieved 2021-01-27.
  18. ^ "RHS Plantfinder - Penstemon 'Osprey' (Bird Series)". Retrieved 2021-01-27.
  19. ^ "RHS Plantfinder - Penstemon hartwegii". Retrieved 2018-04-22.
  20. ^ "RHS Plant Selector Penstemon isophyllus AGM / RHS Gardening". Apps.rhs.org.uk. Retrieved 2021-01-28.
  21. ^ "RHS Plantfinder - Penstemon pinifolius 'Wisley Flame'". Retrieved 2018-04-22.
  22. ^ "RHS Plantfinder - Penstemon rupicola". Retrieved 2018-04-22.
  23. ^ "RHS Plant Selector Penstemon 'Port Wine' AGM / RHS Gardening". Apps.rhs.org.uk. Retrieved 2021-01-28.
  24. ^ "RHS Plant Selector Penstemon 'Raven' AGM / RHS Gardening". Apps.rhs.org.uk. Retrieved 2021-01-28.
  25. ^ "RHS Plantfinder - Penstemon 'Rich Ruby'". Retrieved 2018-04-22.
  26. ^ "RHS Plant Selector Penstemon procerus 'Roy Davidson' AGM / RHS Gardening". Apps.rhs.org.uk. Retrieved 2021-01-30.
  27. ^ "RHS Plant Selector Penstemon 'Rubicundus' AGM / RHS Gardening". Apps.rhs.org.uk. Retrieved 2021-01-30.
  28. ^ "RHS Plant Selector Penstemon 'Schoenholzeri' AGM / RHS Gardening". Apps.rhs.org.uk. Retrieved 2021-01-30.
  29. ^ "RHS Plant Selector Penstemon 'Sour Grapes' M. Fish AGM / RHS Gardening". Apps.rhs.org.uk. Retrieved 2021-01-30.
  30. ^ "RHS Plant Selector Penstemon 'Stapleford Gem' AGM / RHS Gardening". Apps.rhs.org.uk. Retrieved 2021-01-30.
  31. ^ Walters Gardens. Penstemon 'Dark Towers' PP20013
  32. ^ Francis Whittier PennellThe Scrophulariaceae of Eastern Temperate North America, p. 270, at Google Books
  33. ^ Turner, B. L. (2010). Taxonomy of the Penstemon campanulatus complex (Scrophulariaceae) and description of a new species from its midst. Phytoneuron 31 1–5.

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