in section Tvidentatae . Chromatograms of A. higlovii express a marked resemblance to 

 Tridentatae species while demonstrating less similarity toward species of Abrotanvim 

 (figs. 12, 13; unpublished data^) . Consequently, its inclusion in Tridentatae is 

 probably the more accurate arrangement and more indicative of its true relationship. 



Hall and Clements (1923) also suggest that the parent big sagebrush to evolve from 

 A. higlovii was probably A. tvidentata subsp. typiaa (synonymous with subspecies tri- 

 dentata as described by Ward (1953) and Beetle (1960) and as used in the present paper), 

 principally because it appeared to have adapted to environmental conditions under which 

 A. higlovii grew. Chromatographic evidence in the present study substantiates this view 

 and suggests that the parental big sagebrush stock was probably subgroup tvidentata lie 

 or unknown taxa having similar chromatographic characteristics to this subgroup (fig. 

 40) . Chromatograms of A. higlovii and subgroup tvidentata lie are strikingly similar. 

 Spot 9 is small in both, although somewhat more brilliant in A. higlovii. Chromatograms 

 of A. higlovii contain a large and intensely violet spot 14 and a bright blue-green spot 

 92. Of the seven chromatographic subgroups of big sagebrush, subgroup tvidentata lie 

 alone exhibits this same combination of spots. In all other subgroups, spot 14 is blue 

 to blue-gray and not usually a prominent part of the chromatogram, and 92 is missing. 

 Furthermore, the wide distribution of tvidentata Ilc-type plants in southerly localities 

 where A. higlovii is also quite commonly found lends emphasis to the likelihood of a 

 past connection between these two forms. Paradoxically, A. higlovii and tvidentata lie 

 exhibit little morphological similarity. Biglow sagebrush is a diminutive form, erro- 

 neously called black sagebrush by many. In contrast, tvidentata lie contains the 

 largest specimens in the section; plants occasionally reach 12 to 15 feet in height. 

 Another significant point that we cannot account for is the fact that grazing animals 

 show high preference for A. higlovii , but low preference for big sagebrush tvidentata lie. 



Subgroup vaseyana la probably arose as an early variant of big sagebrush and 

 probably represents the parent strain of the present-day subspecies vaseyana subgroups 

 (fig. 40). The basis for this conclusion is the chromatographic similarity of this 

 subgroup to other Tvidentatae species. These include A. nova, A. avhuscula, A. cana, 

 A. tvipavtita, A. vothvoakii, and A. longiloha, all of which purportedly evolved from 

 A. tvideyitata. The common occurrence of a brilliantly iridescent spot 9 in chromato- 

 grams of these sagebrush species suggests closer relationship to group I-type plants 

 {A. tvidentata subsp. vaseyana and subsp. wyomingensis) than to group II -types where 

 spot 9 is small and exhibits little iridescence. Furthermore, considering the subgroups 

 of group I, none bears greater chromatographic resemblance to these species than does 

 vaseyana la. Consequently, subgroup vaseyana la seems to be the branch of big sagebrush 

 arising from tvidentata lie and the branch from which other subgroups of group I and 

 most of the section Tvidentatae evolved. From vaseyana la-type plants, which occupy 

 an intermediate elevational habitat, subgroups vaseyana lb and vaseyana Ic probably 

 arose as modifications respectively adapted to elevational zones below and above that 

 of vaseyana la (fig. 40) . 



Avtemisia tvidentata subsp. vaseyana may have arisen before the establishment of 

 big sagebrush within the Great Basin since this form occurs extensively throughout the 

 present range of the A. tvidentata complex. However, the range of vaseyana lb is 

 largely restricted to habitats within the Great Basin; so this ecotype probably origi- 

 nated within this geographical area. 



Our data coupled with that of Beetle and Young (1965) support the hypothesis that 

 A. tvidentata subsp. wyomingensis is derived from subspecies vaseyana and tvidentata 

 of A. tvidentata and ancestral stock not unlike vaseyana subgroups la and/or lb and 

 tvidentata subgroups lib and/or lie (fig. 40). 



^David Hanks. 1969 chromatography information on file at Intermountain Forest and 

 Range Experiment Station, Ephraim, Utah. 



20 



.1 



