Penstemon caespitosus
Penstemon caespitosus in Cochetopa Canyon, southeast of Gunnison, CO and north of Iris, CO

Secure  (NatureServe)
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Clade: Asterids
Order: Lamiales
Family: Plantaginaceae
Genus: Penstemon
Species:
P. caespitosus
Binomial name
Penstemon caespitosus
Varieties[1]
  • Penstemon caespitosus var. caespitosus
  • Penstemon caespitosus var. desertipicti (A.Nelson) N.H.Holmgren
  • Penstemon caespitosus var. perbrevis (Pennell) N.H.Holmgren

Penstemon caespitosus, commonly known as mat penstemon, is a summer blooming perennial flower in the large Penstemon genus. It is a widespread plant from near timberline to the foothills in the Southern Rocky Mountains and Colorado Plateau in North America. It is noted for its ground hugging growth habit and as a plant used in xeriscape and rock gardening.

Description

Penstemon caespitosus, photo taken 10 miles north of Vernal, UT

Penstemon caespitosus is very low growing, usually just 4–5 centimeters tall with the stems laying down and only the tips curving upright.[2][3] Most often individual stems are 2–8 centimeters in length, but occasionally will be 10 centimeters long.[4] Older stems will be woody and have many branches. The stems root at nodes eventually forming solid mat up to 2 meters in width.[3][5] The stems have small backwards pointing (retrorse) hairs giving the stems a rough texture, but not giving them an ashy appearance.[4]

The leaves of Penstemon caespitosus are attached by a short leaf stem to the main stems, rather than to the base of the plant, each stem having 3–20 pairs of leaves. Like the stems they are covered in pointed backwards facing hairs, but they do not hide the green color of the leaves. The leaves are variable in shape from being wider at the end than at the base (blade obovate to spatulate) or fairly narrow and grass like (linear) with a tapered base. Their size range from 2.5-14 millimeters long and 1–4 millimeters wide, though occasionally they may be a long as 21 millimeters. The tips of their leaves can be rounded, narrowly pointed, or even have the leaf's main rib sticking out to form a sharp tip (mucronate).[4]

Penstemon caespitosus, dissected flower

The flowering season is as early as April and as late as July or August.[2][6] The flowers are a variant on the classic penstemon structure of the petals being united into a tube, in this case with five narrow lobes with rounded ends, 4–6.5 mm in length and 1–1.5 mm wide.[4] Overall the flowers are 10–17 millimeters long, though in exceptional cases they may be as long as 21 millimeters with a funnel to bell shape to the tube.[3] As with the leaves and stems they flowers are retrorsely hairy, though they also will have sparse glandular hairs. The externally the flowers are a handsome blue to purplish lavender with reddish violet nectar guides on the petal lobes into the interior. On the lower surface of the flower tube there will be two ridges.[4] The interior of the flower tube is more white-ish in color[3] with the 5–6 millimeter long tube lined with villous hairs.[4] Each flower has four stamens, the longer two stamens will reach or extend slightly beyond the opening of the flower tube. The pollen sacs at the end of the stamens are 0.6–1.2 millimeters in diameter. The hairy staminode for which Penstemon are known 9–12 millimeters long and covered at the end with densely pilose bright golden yellow hairs. The female style is 13–15 millimeters long.[4]

The four lobed seed capsules are relatiely small, 3.5–5 mm long by 3–4 mm wide.[4] One widely recognized speicies, Penstemon crandallii, is similar enough to Penstemon caespitosus to be confused with it.[3]

Taxonomy

The first recorded scientific collection of Penstemon caespitosus was by Thomas Nuttall and is assumed to have been on his expedition to Oregon in 1834.[3] It was named and more completely described by Asa Gray in 1862, but with the then common "correction" to the genus name to Pentstemon.[1] It had also been collected by John C. Frémont during one of his expeditions, but the condition of the specimen when examined by Gray was, "poor".[7] Botanist William A. Weber thought that Penstemon crandallii and its varieties not distinct enough to qualify as species and that it should be synonymized with P. caespitosus.[8] Two subspecies of P. caepitosus have been identified and are recognized by Plants of the World Online (POWO), the USDA Natural Resources Conservation Service PLANTS database (PLANTS), and the Flora of North America (FNA) as of 2023.[1][9][4]

  • Penstemon caespitosus var. caespitosus
  • Penstemon caespitosus var. desertipicti (A.Nelson) N.H.Holmgren
  • Penstemon caespitosus var. perbrevis (Pennell) N.H.Holmgren

Penstemon caespitosus var. caespitosus is the nominate subspecies. Compared to the others it more consistently has stems that turn upwards at the end compared to var. perbrevis and has smaller flowers than var. desertipicti.[5][10] The main differences recorded in the FNA are the leaves are sometimes linear and the pollen sacs are explanate. However, sometimes the leaves of this variety are blade oblanceolate, similar or identical to the other varieties.[11] This variety's range overlaps with var. perbrevis, but does not with var. desertipicti and is recorded by both POWO and PLANTS as growing in Colorado, Utah, and Wyoming.[12][13]

Penstemon caespitosus var. desertipicti was first described by Aven Nelson in 1926 as a separate species, Penstemon desertipicti and then as a subspecies by David D. Keck in 1937.[5] However, a more complete and accurate description was published by Noel H. Holmgren in 1979.[14] The physical characteristic noted by Keck as distinguishing it from var. caespitosus is having much broader flower tubes.[5] In FNA the primary differences recorded are only having blade oblanceolate leaves and never linear, blade obovate, or spatulate leaves as well as having navicular pollen sacs.[15] In 2011 it was found that this variety is 4n, a tetraploid.[16] Both POWO and PLANTS record this variety of P. caespitosus as growing in Utah and Arizona and being absent from the Rocky Mountains, this geographic isolation also being an argument for being a separate subspecies despite physical similarity.[3][14][17]

Penstemon caespitosus var. perbrevis was first described as a subspecies in 1920 by Francis W. Pennell.[10] As with var. desertipicti it was more completely and accurately described by Noel H. Holmgren in 1979.[18] Pennell described the difference from var. caespitosus as being mainly in that the stems do not turn upwards at the ends, but also that it has leaves that are wider at the ends with a longer and narrower base (spatulate).[10] In this the FNA is in agreement, recording the leaves as ranging in shape from blade obovate to spatulate. In addition describes the variety as having navicular to subexplanate pollen sacs in contrast to the other varieties.[19] Both POWO and PLANTS record this variety of P. caespitosus as growing in Utah and Colorado, with PLANTS specifically recording places of overlap in range in Utah and not having specific location information about the subspecies in Colorado.[18][20]

Habitat and distribution

Penstemon caespitosus habitat in Wyoming, Long Creek Mountain

Penstemon caespitosus grows in sagebrush scrublands, juniper savannas, openings in pinyon-juniper woodlands, with scrub oak, ponderosa pine woodlands, forb-grass openings in aspen-conifer communities, and in alpine meadows. Their altitude range is from as low as 1,500 meters (4,900 ft) to as high as 3,500 meters (11,500 ft).[2][3]

Both POWO and PLANTS record Penstemon caespitosus in four western US states, Arizona, Colorado, Utah, and Wyoming.[1][9] Most of the populations in Colorado and Wyoming are located west of the continental divide, but with a few populations found to the east.[3] NatureServe assessed P. caespitosus as globally secure (G5) in 1984. At the state level they assess populations in Colorado as "apparently secure" (S4), Wyoming populations as "imperiled" (S2), and Utah as "critically imperiled" (S1).[21]

Ecology

The specialist bee Osmia brevis, which is an oligolege that only visits Penstemon flowers, was observed visiting Penstemon caespitosus by A.L. McMullen.[22] Penstemon caespitosa is considered important for supporting the pollinators of the rare species Penstemon debilis by United States Fish and Wildlife Service.[23]

Cultivation

Mat penstemon is amenable to cultivation and is widely grown in both Europe and America as a groundcover especially in rock gardens for xeriscaping.[24] It is recommended by the Royal Horticultural Society for planting in crevice gardens.[25] In comparison to Penstemon thompsoniae and Penstemon teucrioides, it is less sensitive to moisture because it evolved to live in less extreme environments in the Rockies.[26] Though more tolerant of moisture than other mat forming species it is, like most penstemons, susceptible to root rot in poorly draining locations. It is especially intolerant of excess moisture immediately after its blooming period.[27] However, it will grow on clay containing soils in dry conditions and is generally healthier on lean soils low in organic matter.[28][2][27] They are quite suitable for a rock garden, but are too vigorously spreading for trough planting with other plants.[26] The seeds of mat penstemon were experimentally germinated using gibberellic acid sprinkled over seeds on wet paper towels at a dosage of approximately 1000 ppm and this resulted in 30% germination after six weeks while there was no germination from cold treatment alone.[29]

A number of named cultivars of the mat penstemon are available in the horticultural trade. 'Claude Barr', also sometimes called 'Denver Botanical Gardens' is a form with smaller rounded leaves. 'Bruce Alexander' is a cultivar with white flowers and yellow-green leaves.[26] 'Waggon wheel' introduced in 2022 by the Plant Select cooperative sponsored by Colorado State University and Denver Botanic Gardens.[30] Mat penstemon is hardy in USDA zones 4–7.[28][31]

References

  1. 1 2 3 4 POWO (2023). "Penstemon caespitosus Nutt. ex A.Gray". Plants of the World Online. Royal Botanic Gardens, Kew. Retrieved 12 May 2023.
  2. 1 2 3 4 "Penstemon caespitosus var. caespitosus". Wolfe Lab. Ohio State University. 2014. Retrieved 18 May 2023.
  3. 1 2 3 4 5 6 7 8 9 Barnett, Don; Barnett, Donnie (2022). Penstemon of Southeastern Colorado. Pueblo, CO: Ethical Desert. pp. 94–99. ISBN 978-0-578-37397-3.
  4. 1 2 3 4 5 6 7 8 9 Freeman, Craig C. (6 November 2020). "Penstemon caespitosus - FNA". Flora of North America. Retrieved 23 May 2023.
  5. 1 2 3 4 Keck, David D. (1937). "Studies in Penstemon IV. The section Ericopsis". Bulletin of the Torrey Botanical Club. 64 (6): 359, 363–364. doi:10.2307/2481121. JSTOR 2481121. Retrieved 19 May 2023.
  6. ↑ Ackerfield, Jennifer (2015). Flora of Colorado (1 ed.). Fort Worth: BRIT press. p. 590. ISBN 978-1-889878-45-4.
  7. ↑ Gray, Asa (May 1862). "Synopsis of the Genus Pentstemon". Proceedings of the American Academy of Arts and Sciences. MIT Press. 6. Retrieved 18 May 2023.
  8. ↑ Weber, William A.; Wittmann, Ronald C. (2012). Colorado Flora: Eastern Slope, Fourth Edition A Field Guide to the Vascular Plants. University Press of Colorado. ISBN 978-1607321408.
  9. 1 2 USDA, NRCS (2023). "Penstemon caespitosus Nutt. ex A. Gray". The PLANTS Database (plants.usda.gov). Greensboro, North Carolina: National Plant Data Team. Retrieved 18 May 2023.
  10. 1 2 3 Pennell, Francis W. (1917). "Scrophulariaceae of the Central Rocky Mountain States". Contributions from the United States National Herbarium. Smithsonian Institution Press. 20 (9): 335, 375. Retrieved 22 May 2023.
  11. ↑ Freeman, Craig C. (5 November 2020). "Penstemon caespitosus var. caespitosus - FNA". Flora of North America. Retrieved 23 May 2023.
  12. ↑ POWO (2023). "Penstemon caespitosus var. caespitosus". Plants of the World Online. Royal Botanic Gardens, Kew. Retrieved 22 May 2023.
  13. ↑ USDA, NRCS (2023). "Penstemon caespitosus Nutt. ex A. Gray var. caespitosus". The PLANTS Database (plants.usda.gov). Greensboro, North Carolina: National Plant Data Team. Retrieved 22 May 2023.
  14. 1 2 POWO (2023). "Penstemon caespitosus var. desertipicti (A.Nelson) N.H.Holmgren". Plants of the World Online. Royal Botanic Gardens, Kew. Retrieved 19 May 2023.
  15. ↑ Freeman, Craig C. (5 November 2020). "Penstemon caespitosus var. desertipicti - FNA". Flora of North America. Retrieved 23 May 2023.
  16. ↑ Broderick, Shaun R.; Stevens, Mikel R.; Geary, Brad; Love, Stephen L.; Jellen, Eric N.; Dockter, Rhyan B.; Daley, Shawna L.; Lindgren, Dale T. (February 2011). "A survey of Penstemon's genome size". Genome. 54 (2): 160–173. doi:10.1139/G10-106. PMID 21326372. Retrieved 19 May 2023.
  17. ↑ USDA, NRCS (2023). "Penstemon caespitosus Nutt. ex A. Gray var. desertipicti (A. Nelson) N.H. Holmgren". The PLANTS Database (plants.usda.gov). Greensboro, North Carolina: National Plant Data Team. Retrieved 22 May 2023.
  18. 1 2 POWO (2023). "Penstemon caespitosus var. perbrevis (Pennell) N.H.Holmgren". Plants of the World Online. Royal Botanic Gardens, Kew. Retrieved 22 May 2023.
  19. ↑ Freeman, Craig C. (5 November 2020). "Penstemon caespitosus var. perbrevis - FNA". Flora of North America. Retrieved 23 May 2023.
  20. ↑ USDA, NRCS (2023). "Penstemon caespitosus Nutt. ex A. Gray var. perbrevis (Pennell) N.H. Holmgren". The PLANTS Database (plants.usda.gov). Greensboro, North Carolina: National Plant Data Team. Retrieved 22 May 2023.
  21. ↑ NatureServe (2023). "Penstemon caespitosus". NatureServe Explorer. Arlington, Virginia: NatureServe. Retrieved 27 May 2023.
  22. ↑ Tepedino, V.J.; Griswold, T.L.; Freilich, J.E.; Shephard, P. (December 2011). "Specialist and Generalist Bee Visitors of an Endemic Beardtongue ( Penstemon caryi: Plantaginaceae) of the Big Horn Mountains, Wyoming". Western North American Naturalist. 71 (4): 527. doi:10.3398/064.071.0410. S2CID 56266655. Retrieved 26 May 2023.
  23. ↑ 77 FR 48368
  24. ↑ Shonle, I.; Vickerman, L.G.; Klett, J.E. (April 2014). "Native Herbaceous Perennials for Colorado Landscapes - 7.242". Colorado State Extension. Colorado State University. Retrieved 25 May 2023.
  25. ↑ "RHS Advice". Garden. Royal Horticultural Society. 139 (7): 28. July 2014.
  26. 1 2 3 Way, David; James, Peter (1998). The gardener's guide to growing penstemons. N: David & Charles. pp. 29, 85. ISBN 978-0-88192-424-4.
  27. 1 2 "Penstemon caespitosus - mat penstemon". Garden Explorer. Santa Fe Botanical Garden. 2023. Retrieved 25 May 2023.
  28. 1 2 "Penstemon caespitosus". Missouri Botanical Garden Plant Finder. Missouri Botanical Garden. Retrieved 19 May 2023.
  29. ↑ Love, Stephen L; Akins, Candace J (2020). "Fifth summary of the native seed germination studies of Norman C Deno: species with names beginning with letters P and Q". Native Plants Journal. 21 (1): 88. doi:10.3368/npj.21.1.83. S2CID 241374952.
  30. ↑ Langelo, Linda (18 January 2022). "Plant Select 2022 New Introductions". Morning Ag Clips. Retrieved 19 May 2023.
  31. ↑ Kelsey, Amber (21 September 2017). "Penstemon Plant List". Garden Guides. Retrieved 25 May 2023.
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