29 



C. Disease, predation, or grazing: Rhinocyllus conicus 

 was introduced as a biological control for musk 

 thistle ( Carduus nutans ) , but also infests Cirsium 

 lonqistylum . The impact of the weevil on the 

 fecundity of Cirsium lonqistylum has not been 

 determined. 



D. Inadequacy of existing regulatory mechanisms: None 

 known . 



E. Other natural or man-made factors: None known. 

 II. ASSESSMENT AND RECOMMENDATIONS 



12. General assessment of vigor, trends, and status: Cirsium 

 lonqistylum is currently known only from locations in the 

 Little Belt Mountains, with one location in the Big Belt 

 Mountains of Montana. Populations are extensive and 

 appear quite vigorous. A weevil introduced as a 

 biological control for Carduus nutans is also infesting 

 C. lonqistylum , but the impacts on the fecundity of the 

 plant are not known. 



13. Recommendations for listing or status change. 



A. Recommendation to U.S. Fish and Wildlife Service: 



On the basis of current information summarized in 

 this status report, it is recommended that Cirsium 

 lonqistylum be retained in Category 2. Although 

 population sizes of this Montana endemic are large, 

 the extent of the threat posed by the weevil 

 Rhinocyllus conicus is not known. Further work is 

 needed to clarify this threat, and resolve the 

 taxonomic status of this species. 



B. Recommendations to other U.S. federal agencies: It 



is recommended that Cirsium lonqistylum be 

 maintained on the U.S. Forest Service list of 

 sensitive plant species until the taxonomic status 

 and measurement of threat posed by the weevil 

 Rhinocyllus conicus are resolved. 



C. Other status recommendations. 



1. Counties and local areas: No recommendations. 



2. States: Cirsium lonqistylum will be listed as 

 S3 (found abundantly in a restricted range) on 

 the 1991 Montana Natural Heritage Program list 

 of plant species of special concern. 



