Table ^ .--Flowering dates of the ahromatographia subgroups of 



A. tridentata 



Subgroup 



Flowering date 



vaseyana Ic 



July 15-30 



vaseyana la 



August 5-20 



vaseyana lb 



September 7-21 



wyomingensis Id 



September 7-21 



tridentata I la 



September 7-21 



tridentata lib 



September 10-October 10 



tridentata lie 



September 10-October 10 



One of the primary genetic modifications necessary to permit the development of 

 short- growing- season strains in high elevations is the ability to reproduce under pre- 

 vailing conditions. Of interest in this regard is the early flowering of vaseyana Ic 

 and vaseyana la in contrast to the other subgroups. All seven subgroups are growing 

 together at Snow College Field Station, Ephraim, Utah (5,600 feet elevation). Here, 

 vaseyana Ic blooms as early as mid-July and vaseyana la by early August, whereas the 

 other subgroups are not in flower until after the first week of September (table 4). 

 Phenological data presented here are in general agreement with observations from 

 uniform gardens in northern Idaho (Winward 1970) and south central British Columbia 

 (Marchand and others 1966). The Canadian investigators found, as we did, early- and 

 late-flowering ecotypes of A. tridentata subsp. vaseyana. 



The dominant low-elevation valley big sagebrush {A. tridentata subsp. tridentata) 

 of the northern Great Basin is tridentata lib; in the southern Great Basin, however, 

 tridentata lie is the common low-elevation valley big sagebrush. Small populations of 

 lie can frequently be seen throughout the Great Basin as tall shrubs growing along 

 fence rows or in other protected areas. Tridentata lib predominates in most low- 

 elevation big sagebrush sites, but it is not confined to these areas; it can be found 

 elsewhere in small populations intermixed with vaseyana la and vaseyana lb types, 

 particularly in the lower foothill areas. 



Subgroup tridentata Ila was collected only from localized areas of northwestern 

 Nevada where it grows in close association with A. tridentata subsp. hniomingensis (Id). 

 In fact, chromatographically , it appears to have arisen from hybridization between 

 wyomingensis Id and tridentata lib since it contains characteristics common to both 

 (fig. 6). 



There is abundant chromatographic evidence that where populations of subgroups 

 overlap and intermix, interbreeding occurs. This is particularly evident in ecotonal 

 areas between populations of vaseyana lb and tridentata lib; chromatograms of many 

 specimens contain unusual combinations of spots not found in isolated, uniform popula- 

 tions of either subgroup (fig. 34). 



The distribution of subgroups is so uniform within the Great Basin that rather 

 accurate predictions as to their presence can frequently be made after considering ele- 

 vation and topography. However, distribution outside this area appears to be more er- 

 ratic. For instance, only a few specimens of subgroup vaseyana lb have been collected 

 from areas peripheral to the Great Basin. Collection sites outside this area, physi- 

 cally similar to those within the Great Basin in which this subgroup is characteristic, 

 are usually occupied by vaseyana la, the most widely distributed of the A. tridentata 

 subsp. vaseyana subgroups. Furthermore, A. tridentata subsp. wyomingensis , widely 



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