Scientific Name : Pediocactus knowltonii
Author : L. Benson
NatureServe Explorer
Common Name : Knowlton's Cactus
Current Research Activities
1997 profile
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Taxonomy
Cactaceae (cactus family)
Ranks and Status
State Rank : SU
State Rank Reason : There are no known occurrences of Pediocactus knowltonii within Colorado (USA). There have been reports of the plant occurring near the state line in Archuleta County, however, this is probably based on erroneous location information. Nonetheless, the proximity of the New Mexico occurrences indicate that its range may well extend into Colorado but has not yet been detected.
U.S. Endangered Species Act : ESA Endangered
Colorado Threatened and Endangered List : none
Other Statuses : SWAP Tier 1
Description and Phenology
General Description:
Pediocactus knowltonii is a small cactus with either clustered or solitary stems measuring up to 5.5 centimeters (cm) tall and 3 cm in diameter (USFWS 2021). The yellow centered, pink flowers, are generally bigger than the plant itself (Olwell 1986).
Look Alikes:
The common Pediocactus simpsonii is well over 5 cm in diameter and has a dark reddish-brown central spine. P. knowltonii is extremely inconspicuous except in flower (pers. comm. Coles 1994). The plants flower for only a few days and shrink afterwards. They are the diameter of a quarter or smaller (less than 3 cm across) (pers. comm. Jennings 1995). Recognized by minute radial spines on tuburcles; white, yellow, pink, or rarely magenta flowers on top of the plant.
Phenology:
Flowering occurs in early May with fruits ripening in June and occasionally into early July (USFWS 2021).The flowers open by mid-morning and close in late afternoon, and generally last 2-3 days (Heil 1985).
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Habitat
Pediocactus knowltonii grows on the eastern edge of the Colorado Plateau on tertiary alluvial deposits that form rolling gravelly hills covered with Colorado pinyon, Rocky Mountain juniper and sagebrush (Olwell 1986).
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Elevation Range:
6,000 - 6,300 feet (1,829 - 1,920 meters)
Distribution
Colorado Endemic:
No
Range:
There are no known occurrences of Pediocactus knowltonii within Colorado. This species has been recorded in Rio Arriba and San Juan counties in New Mexico, USA. Weber and Wittman (1996) report the plant as occurring near the state line in Archuleta County, Colorado however, this is probably based on erroneous location information on a specimen label. Nonetheless, the proximity of the New Mexico occurrences indicate that its range may well extend into Colorado but has not yet been detected.
Threats and Management Issues
This species is considered to have low adaptive capacity and is expected to be highly 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. Botanical Research Institute of Texas, Fort Worth, TX. 818 pp.
- Butterworth, C., and J.M. Porter. 2013. Pediocactus knowltonii. IUCN Red List of Threatened Species. Version 2013.1. Online. Available: http://www.iucnredlist.org (accessed 11 July 2013).
- Colorado Native Plant Society. 1989. Rare plants of Colorado. Rocky Mountain Nature Association, Colorado Native Plant Society, Estes Park, Colorado. 73 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.
- Cully, A. 1996. Knowlton's Cactus (Pediocactus knowltonii) Reintroduction. A chapter in Restoring Diversity, strategies for reintroduction of endangered plants. Editors Falk, D.A., C.I. Miller, and M. Olwell. Island Press.
- Flora of North America Editorial Committee, ed. (FNA). 1993+. Flora of North America North of Mexico. Oxford Univ. Press, New York, Oxford.
- Gucker, C. L. 2007. Pediocactus knowltonii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [2011, March 30].
- Handwerk, J., L. Grunau, and S. Panjabi. 2015. Colorado Wildlife Action Plan: 2015 Rare Plant Addendum. Colorado Natural Heritage Program, Colorado State University, Fort Collins, Colorado, USA.
- Heil, K. 1985. Knowlton cactus (Pediocactus knowltonii) recovery plan. Unpublished report prepared for the US Fish and Wildlife Service, Albuquerque, NM.
- Heil, K., B. Armstrong and D. Schleser. 1981. A review of the genus Pediocactus. Cactus and Succulent Journal 53:17-39.
- McDonald, C., and D.J. Ferguson. 2008. New Mexico rare plants: Pediocactus knowltonii (Knowlton cactus). New Mexico Rare Plant Technical Council, Albuquerque, New Mexico. Online. Available: http://nmrareplants.unm.edu (Accessed 2013).
- Neely, B., S. Panjabi, E. Lane, P. Lewis, C. Dawson, A. Kratz, B. Kurzel, T. Hogan, J. Handwerk, S. Krishnan, J. Neale, and N. Ripley. 2009. Colorado Rare Plant Conservation Strategy, Developed by the Colorado Rare Plant conservation Initiative. The Nature Conservancy, Boulder, Colorado, 117 pp.
- New Mexico Native Plant Protection Advisory Committee. 1984. A handbook of rare and endemic plants of New Mexico. Univ. New Mexico Press, Albuquerque. 291 pp.
- Olwell, P. 1986. Audubon wildlife report. National Audubon Society, New York, NY.
- Rocky Mountain Society of Botanical Artists. 2009. RARE Imperiled Plants of Colorado, a traveling art exhibition. Exhibition catalogue developed by the Denver Botanic Gardens and Steamboat Art Museum.
- Sivinski, R. 2005. Knowlton's Cactus (Pediocactus knowltonii): Progress Report by Robert Sivinski, NM Forestry Division for U.S. Fish and Wildlife Service, Region 2, Section 6, Segment 19. September 30. 13pp.
- Sivinski, R. C. and C. McDonald. 2004a. Knowlton's cactus (Pediocactus knowltonii): Eighteen years of monitoring and recovery actions. Pages 98-107 in P. Barlow-Irck, J. Anderson, C. McDonald, eds. Southwestern rare and endangered plants: Proceedings of the Fourth Conference; March 22-24, 2004, Las Cruces, NM. Proceedings. RMRS-P-48CD. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. Accessed online on May 11, 2011 at: http://www.treesearch.fs.fed.us/pubs/29594
- Spackman, S., B. Jennings, J. Coles, C. Dawson, M. Minton, A. Kratz, and C. Spurrier. 1997. Colorado rare plant field guide. Prepared for Bureau of Land Management, U.S. Forest Service and U.S. Fish and Wildlife Service by Colorado Natural Heritage Program.
- Stafford, R. 1989. Botanists find cactus better neighborhood. Plant Conservation 4(1): 3.
- U.S. Fish and Wildlife Service (USFWS). 2010. Knowlton's Cactus (Pediocactus knowltonii) 5-year review: summary and evaluation. U.S. Fish and Wildlife Service, New Mexico Ecological Field Services Office, Albuquerque, NM. 16 pp.
- 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, Western Slope, A Field Guide to the Vascular Plants, Fourth Edition. Boulder, Colorado. 532 pp.
