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26 



population size fluctuations. Monitoring data 

 currently indicate that populations contained a good 

 mix of both rosettes and flowering plants. It is 

 possible that infestation rates are not high enough 

 to limit this species, or that the Cirsium 

 lonqistylum populations have very few predatory 

 fauna; a hypothesis put forth by Dr. C. Turner 

 (U.S.D.A., Albany, CA, pers. coram.). 



2. Competition. 



a. Intraspecif ic\Interspecif ic: No studies 

 have been done on competitive 

 interactions, either intraspecif ic or 

 interspecific. However, the frequent 

 occurrence of C. lonqistylum in disturbed 

 sites and in open, unshaded areas suggests 

 that it is not very tolerant of shading. 



Hybridization. 



1. Naturally occurring: Variation of some local 

 populations in both leaf and involucral 

 characters has been interpreted to indicate 

 hybridization between C. lonqistylum and 

 perhaps C. hooker ianum , which has been reported 

 from the area (Ownbey 1987, Shelly 1986) . 

 Similarities to C. scariosum have also been 

 noted (Moore and Frankton 1963) . The incidence 

 of these variant plants seems to be greater in 

 disturbed sites than in undisturbed sites 

 (Shelly 1986) , which is a common pattern in 

 many cases of hybridization (Anderson 1953) . 

 More recently, Ownbey (1990) has stated that he 

 thinks the variation "can be ascribed to 

 intraspecif ic genetic variation" rather than 

 hybridization. There is also some question 

 about the identity of the plants from the area 

 that were reported as C. hookerianum (Cronquist 

 1991) . Thus, there are currently unresolved 

 questions about the status of this species and 

 further study is needed. 



2. Artificially induced: None known. 



3. Potential in cultivation: Not known, although 

 seeds appear to germinate readily, plants are 

 not in cultivation. 



