DISCUSSION 



Evidence for the great plasticity of the Tridentatae complex and particularly of 

 big sagebrush, suggested by Hall and Clements (1923) and further demonstrated by the 

 cytogeographic studies of Ward (1953) , is substantiated by the large number of 

 chromatographic variants resulting from this study. 



Greatest chromatographic variation was observed among collections of big sagebrush; 

 at least seven rather distinct patterns were identified. Considerable additional 

 variation was found among individual chromatograms of collections of this species, but 

 these could not be associated with meaningful patterns. Similar multiple patterns 

 (table 1) and incidental variation were found among collections of other species and sub- 

 species, but none of these approached the apparent chemical diversity of /I. tridentata. 



The most common departure from regular chromatographic patterns seemingly resulted 

 from interbreeding between Tridentatae species or subspecies . Chromatograms of progeny 

 from naturally occurring hybrids could be identified by the appearance of spots specific 

 for one parent species in the otherwise normal chromatogram of another species. The most 

 common example of this phenomenon was the occurrence of traces of spot 19 from A. nova 

 or A. cana subsp. viscidula in approximately one-fourth of the A. tridentata subsp. 

 tridentata and vaseyana collections. In support of this contention. Beetle (1960) 

 reported considerable evidence of A. nova in the morphological characteristics of big 

 sagebrush populations on the Shivwitts Indian Reservation, Washington County, Utah. 

 Chromatograms of collections from this vicinity, which were included in this study, 

 contained a rather prominent spot 19, which supports Beetle's observation as to close 

 relationship of this form to A. nova. Further evidence of past hybridization was the 

 appearance of spot 20, specific for A. tripartita subsp. tripartita in approximately 

 20 percent of the collections of subgroup la of A. tridentata vaseyana (fig. 33). Tliis 

 spot was observed in widely scattered populations of subgroup vaseyana la from south- 

 western Idaho to southern Utah. Usually, the introgression shown by chemical patterns 



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