CPC Plant Profile: Rocky Mountain Thistle
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Plant Profile

Rocky Mountain Thistle (Cirsium perplexans)

  • Global Rank: G2 - Imperiled
  • Legal Status: N/A
  • Family: Asteraceae
  • State: CO
  • Nature Serve ID: 142607
  • Date Inducted in National Collection:

A native thistle, endemic to Colorado. Cirsium perplexans is an erect perennial or biennial, 2 to 6 dm tall. Stems are often purplish and slightly tomentose. Leaves are toothed with short weak spines, glabrate above, and tomentose below. Upper leaves are clasping at the base. Flowers are purple to red. Flower heads are solitary on the stem or branches, and they are about 2.5 to 3.5 cm high and about as wide (Rydberg 1905, Harrington 1954). Lyon notes from her field observations that this species is not rhizomatous (Colorado Natural Heritage Program 2004).

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Nature Serve Biotics
  • 05/02/2017

This is a Colorado endemic known from 43 locations. The species is threatened by biocontrol and other control efforts aimed at non-native thistles.

(Rydb.) Petrak, Mary VB Goshorn
  • 01/01/2010

The primary threats to C. perplexans include the use of biological control and herbicides in the management of non-native Cirsium species, invasions of non-native plant species, and impacts from recreational, agricultural, industrial, and residential land

(Rydb.) Petrak, Mary VB Goshorn
  • 01/01/2010

There are 29 principal occurrences documented in the Colorado Natural Heritage Program database. Five of the 29 occurrences have not been observed in over 20 years. The USFS Conservation Assessment documents 25 occurrences (Spackman Panjabi and Anderson 2004). Four new occurrences have been documented since the Assessment was published.

(Rydb.) Petrak, Mary VB Goshorn
  • 01/01/2010


(Rydb.) Petrak, Mary VB Goshorn
  • 01/01/2010

On USFS Sensitive Species list

(Rydb.) Petrak, Mary VB Goshorn
  • 01/01/2010

Present research priorities include gathering baseline data on the distribution and population sizes for Cirsium perplexans. Identifying high quality occurrences of C. perplexans in which the size, condition, and landscape context are excellent will also help to prioritize conservation efforts for C. perplexans (Panjabi and Anderson 2004). Understanding the breeding systems employed by Cirsium perplexans is another research priority for this species due to the practical and scientific value of such studies. Answers to questions about whether C. perplexans is apomictic or a frequent outcrosser will provide needed guidance for developing appropriate management practices. If C. perplexans reproduces predominantly through apomixis, the genetic population structure is more stable than if the species is an outcrosser, since a pollinator is not required. Thus, a trail or road through an apomictic population will not be as detrimental as one through a population of outcrossers (Panjabi and Anderson 2004). The response of Cirsium perplexans to human impacts and disturbance has not been studied. Gaining practical knowledge of how to best manage populations of this species is of considerable importance given the rapid change in land use patterns, increasing recreational use, and increasing human population density of Colorados western slope communities (Panjabi and Anderson 2004).

(Rydb.) Petrak, Mary VB Goshorn
  • 01/01/2010

Seed collection and storage.


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Taxon Cirsium perplexans
Authority (Rydb.) Petrak
Family Asteraceae
CPC Number 6169
ITIS 36399
Common Names Rocky Mountain Thistle | spring thistle
Associated Scientific Names Cirsium perplexans | Cirsium vernale | Carduus americanus var. perplexans | Carduus arvensis var. albiflorus | Carduus perplexans | Carduus vernalis
Distribution Colorado endemic known from Delta, Mesa, Montrose, Gunnison, Garfield, and Ouray counties in the Colorado and Gunnison River Valleys. Estimated range is 4,981 square kilometers (1,923 square miles).
State Rank
State State Rank
Colorado S2S3

Cirsium perplexans is found almost exclusively on clay soils or adobe hills (Weber and Wittmann 2001b) that are derived from shales of the Mancos or Wasatch formations (Lyon personal communication 2003). Adobe hills are a local term for barren outcrops of clay soils (Foutz 1994), which are common in western Colorado.Overall, Cirsium perplexans tends to grow in dry, sparsely vegetated or disturbed areas. It has been described as occurring adjacent to a drainage and a dry wash and along roads, usually infrequently used roads. Populations found along roads were thought to be moving into the habitat created by the roads (Lyon personal communication 2003). Cirsium perplexans is found across an approximately 3,000 foot elevational range, within sites in montane shrublands or woodlands. The range of elevation documented in Element Occurrence Records of the Colorado Natural Heritage Program (2004) is 5,800 feet (at the Plateau Creek State Wildlife Area) to 8,060 feet (at Cimarron State Wildlife Area). Cirsium perplexans has been described as occurring in sites with south, west, and east exposure (Colorado Natural Heritage Program 2004). Lyon (personal communication 2003) has found C. perplexans on all aspects and on flat sites.

Ecological Relationships


Common Name Name in Text Association Type Source InteractionID
Lead Institution State Reintroduction Type Year of First Outplanting

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