Cirsium lonqistylum is strongly separated from both C. 

 scariosum and C_^ hookerianum . Cirsium scariosum from Montana is 

 distinct from the samples from Nevada and Oregon. Similarly, C. 

 hookerianum samples from British Columbia and northern Montana 

 separate from westcentral Montana samples. Hybrids as a group 

 are scarcely distinguishable from C_^ lonqistylum and C. 

 hookerianum . 



DISCUSSION 



Enzyme Electrophoresis Analysis - The Cirsium samples we 

 analyzed contain levels of enzyme variability that would be 

 expected, based on data from other species with similar life 

 history characteristics (Hamrick & Godt 1989) . Whether data is 

 sorted and analyzed by taxonomic classification or 

 population/locality, similar results are obtained. Plants 

 identified in the field as Cirsium longistylum are genetically 

 distinct from plants identified as C^ hookerianum and C. 

 scariosum . Indeed, of the three species sampled from westcentral 

 Montana, C^ lonqistylum appears to be the most genetically 

 distinct. Three populations that are considered to be pure or 

 nearly pure C_^ lonqistylum cluster together in our analysis, and 

 are very distinct from populations of Cj_ hookerianum and C. 

 scariosum , which appear more closely related. All plants 

 classified as hybrids of C^;. lonqistylum cluster with pure C. 

 lonqistylum . whereas populations composed of a mixture of parents 

 and putative hybrids are heterogeneous - two cluster with C. 

 lonqistylum , one clusters with C^ hookerianum . and one clusters 

 with C^ scariosum . 



While these results are consistent with the hypothesis that 

 hybridization is occurring between C^ lonqistylum and another 

 species, enzyme electrophoresis does not provide enough 

 diagnostic genetic markers to rule out alternative explanations. 



DNA Analysis - Preliminary results of the analysis of RAPD 

 data are congruent with electrophoretic results, and also provide 

 additional insights into Cirsium genetics. Plants identified as 

 Cirsium lonqistylum are separable from all others, but exhibit 

 more variability than other species within westcentral Montana. 

 Several of the C^ lonqistylum samples are among the most 

 genetically distinct plants that we analyzed, suggesting that C. 

 lonqistylum represents a well-differentiated evolutionary 

 lineage. Whether the variability within C^ lonqistylum is 

 attributable to hybridization requires more detailed 

 investigation. 



Two widely separated northern samples of C^ hookerianum . 

 obtained from herbarium specimens, are similar to each other, but 

 differentiated from westcentral Montana samples. Based on 

 morphology, Cronquist (1964) considered northern C_^ hookerianum 



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