EXECUTIVE SUMMARY 



A genetic analysis of Cirsium longistylum (Long-styled thistle) , 

 a candidate threatened plant species, was initiated in 1993 to 

 investigate hypothesized hybridization with C^ hookerianum . The 

 objective of the analysis was to determine if C^ longistylum is a 

 genetically unique entity, and to assess the importance of 

 introgression in the evolution of the species. Enzyme 

 electrophoresis was performed on 150 individuals from 12 

 populations of westcentral Montana. Cirsium longistylum was 

 found to be genetically distinct from Montana populations of C^ 

 hookerianum and C^ scariosum . Putative hybrids of C^ longistylum 

 were found to be most similar to "pure" C^ longistylum plants, a 

 finding consistent with either a hypothesis of hybridity or high 

 natural variability within C^ longistylum . A preliminary 

 analysis of randomly amplified polymorphic DNA (RAPD) was 

 initiated to gain better resolution of genetic relationships 

 among C^ longistylum , putative hybrids, and closely related 

 Cirsium species. Twentyone samples representing C^ longistylum , 

 C. hookerianum , C. scariosum , and putative hybrids were analyzed, 

 including four samples of C^ hookerianum and C^. scariosum from 

 outside the study area in westcentral Montana. The RAPD data was 

 congruent with electrophoretic data in identifying Cirsium 

 longistylum as genetically distinct. Cirsium hookerianum and C^ 

 scariosum sampled outside the region were found to be genetically 

 distant from samples of the same species in westcentral Montana. 

 These data suggest that introgression historically may have 

 occurred among all three species of the region. In order to 

 document introgression using RAPD markers, a thorough 

 understanding of the genetic composition of "pure" C^ hookerianum 

 and C^ scariosum from outside the region is required. In 

 addition, phylogenetic and additional morphological analyses are 

 proposed as a basis for future conservation and management 

 decisions. 



