Scientific Name : Penstemon laricifolius ssp. exilifolius
Author : (A. Nels.) Keck
NatureServe Explorer
Common Name : Larch- leaf Beardtongue
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Taxonomy
Plantaginaceae (plantain family)
Ackerfield (2015, 2022) and others place the genus Penstemon in the Plantaginaceae or the Plantain Family.
Ranks and Status
State Rank : S2S3
State Rank Reason : Penstemon laricifolius ssp. exilifolius is known from about 15 occurrences in northern Larimer and Jackson counties, Colorado, USA. Road maintenance and motorized recreation are potential threats as well as competition from invasive plant species and the effects of climate change.
U.S. Endangered Species Act : none
Colorado Threatened and Endangered List : none
Other Statuses : SWAP Tier 2
Description and Phenology
General Description:
Penstemon laricifolius ssp. exilifolius is a perennial with several to numerous stems arising 10 to 20 (34) cm from a branched caudex. Leaves are numerous, narrowly linear to filiform, 15 to 25 mm long, and in dense, erect clusters on the caudex. Flowers are borne in a narrow inflorescence, few- to many-flowered; pedicels slender, sepals lanceolate and long-acuminate, with scarious margins. Corolla is white, greenish white, or light rose outside, somewhat abruptly inflated, 12 to 15 mm long, with glabrous anthers that dehisce their full length and at the suture; the sterile filament is very stiffly and densely short-pubescent. Inflorescence is a raceme with 1 (few) flowers per node and nodes that are slightly overlapping to remote (Heidel and Handley 2007, Ackerfield 2017).
Look Alikes:
The filiform leaves and small white flowers are distinctive.
Phenology:
Flowers late June through August. Fruiting in August (Colorado Natural Heritage Program occurrence records).
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Habitat
In Colorado, this subspecies is found in grasslands and sagebrush meadows (Ackerfield 2015). Associated taxa include: Artemisia spp., Festuca idahoensis, Artemisia frigida, Chrysothamnus viscidiflorus, Muhlenbergia montana, Bouteloua gracilis, Eriogonum umbellatum, Lupinus argenteus, Oxytropis sericea, and Sedum lanceolatum.
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Elevation Range:
7,590 - 9,406 feet (2,314 - 2,867 meters)
Distribution
Colorado Endemic:
No
Range:
Penstemon laricifolius ssp. exilifolius is known from Larimer and Jackson counties, Colorado, USA. Estimated range extent in Colorado of 535 square kilometers was calculated in GeoCAT using occurrence data provided by the Colorado Natural Heritage Program (2024). This species can also be found in Wyoming, USA.
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Threats and Management Issues
In Colorado, many of the occurrences are found along roadsides and seem to tolerate the associated disturbance, however, invasive species have been reported at five of these occurrences and may begin to compete with the Penstemon. Approximately one third of the occurrences report livestock grazing within occupied habitat but the species appears to be somewhat compatible with it. One occurrence reports a nearby housing development as a potential threat, another reports recreational use as a potential threat, and one reports powerline work as a potential threat. This species is considered to have moderate adaptive capacity and is expected to be slightly to moderately vulnerable to climate change under both RCP 4.5 and 8.5 scenarios, as assessed for the 2025 Colorado State Wildlife Action Plan (CNHP 2025).
References
- Ackerfield, J. 2015. Flora of Colorado. BRIT Press, Botanical Research Institute of Texas, Fort Worth, TX. 818 pp.
- Ackerfield, J. 2022. Flora of Colorado. Second Edition. Bot. Misc. 60. BRIT Press, Fort Worth Botanic Garden/Botanical Research Institute of Texas, U.S.A. 861 pp.
- Colorado Natural Heritage Program (CNHP). 2025. Climate Change Vulnerability Assessment of Colorado Tier 1 and Tier 2 Plant Species of Greatest Conservation Need (SCGN) for the 2025 Colorado State Wildlife Action Plan. Colorado Natural Heritage Program, Colorado State University, Fort Collins.
- Colorado Natural Heritage Program and the Geospatial Centroid. 2017. The Colorado Ownership and Protection Map (COMaP). Colorado State University, Ft. Collins, CO.
- Dorn, R. D. 2001. Vascular Plants of Wyoming. 3rd edition. Mountain West Publishing. Cheyenne, Wyoming. 412 pp.
- Harrington, H. D. 1954. Manual of the Plants of Colorado. Sage Books, Denver, CO. 666 pp.
- Heidel, B. and J. Handley. 2007. Penstemon laricifolius Hook. & Arn. ssp. exilifolius (A. Nels.) D.D. Keck (larchleaf beardtongue): a technical conservation assessment. [Online]. USDA Forest Service, Rocky Mountain Region. Available: http://www.fs.fed.us/r2/projects/scp/assessments/penstemonlaricifoliussspexilifolius.pdf.
- Keck. 1937. Studies in Penstemon. Bulletin of the Torrey Club. Vol. 64.
- USDA, Natural Resources Conservation Service, PLANTS Database [USDA PLANTS]. http://plants.usda.gov/. Accessed 2017.
- USDA, NRCS. 2022. The PLANTS Database. National Plant Data Team, Greensboro, NC 27401-4901 USA.
- Weber, W. A. and R. C. Wittmann. 2012. Colorado Flora, Eastern Slope, A Field Guide to the Vascular Plants, Fourth Edition. Boulder, Colorado. 555 pp.
