INTRODUCTION 



Cirsium lonaistvlum Moore & Frankton (Long-styled thistle) 

 is a species endemic to four "island" mountain ranges of 

 westcentral Montana, currently placed in Category 2 by the U.S. 

 Fish and Wildlife Service as a candidate for federal listing as 

 threatened (58 FR51144). 



Cirsium lonqistvlum is one of six closely related species of 

 thistle distributed in the Rocky Mountains. Cirsium hookerianum 

 Nutt. is primarily distributed in British Columbia and Alberta, 

 but extends southward into westcentral and western Montana where 

 it occurs sympatrically with C^ lonqistylum in the Big Belt and 

 Little Belt Mountain Ranges. Two additional species, Cirsium 

 scariosum Nutt. and C. tweedyi (Rydb.) Petrak, approach the range 

 of C^ lonqistvlum from the southwest. Cirsium scopulorum 

 (Greene) Cockerell and C. eatonii (A. Gray) Robinson (Moore and 

 Frankton 1965) occur south of Montana in the southern Rocky 

 Mountains. 



Survey and monitoring work has been conducted to 

 characterize distribution and life history of Cirsium lonqistvlum 

 (Schassberger 1991, Schassberger and Achuff 1991, Roe 1992, Poole 

 and Heidel 1993, Heidel 1994). At many sites, plants with bract 

 characteristics deviating from the taxonomic circumscription of 

 Moore and Frankton (1963) were noted. One of the three 

 monitoring sites (Neihart) was interpreted as consisting 

 primarily of Cirsium hookerianum . possibly with C. hookerianum x 

 C. lonqistvlum hybrids present (Cronquist pers. commun. as cited 

 in Roe 1992) . Monitoring work of the following year included an 

 expanded morphological investigation (Poole and Heidel 1993). 

 This investigation revealed that some populations contained 

 plants with the diagnostic bract characteristics of both C. 

 lonqistvlum and C^ hookerianum . Based on morphology it was 

 concluded that Cirsium lonqistylum appeared to be a distinct 

 species that hybridizes freely with C. hookerianum , producing 

 swarms of morphologically variable individuals. This provisional 

 interpretation warranted genetic documentation, and the present 

 study was initiated to test the discreetness and persistence of a 

 recognizable Cirsium lonqistylum genome. 



