1 ' \ 



Figure 45. — Differential deer 

 browsing on subspecies of 

 rubber rabbitbrush on Bald 

 Mountain^ Sanpete Co., Utah. 

 The dxxrk plant (lower left) 

 is the threadleaf rubber 

 rabbitbrush (C. nauseosus 

 ssp. consimilis/'j wheareas 

 the light plant (center) is 

 white rubber rabbitbrush (c. 

 nauseosus ssp. albicaulisJ. 



permanent, dense, white to grayish tomentum (fig. 47). The leaves are 2.5 to 4 cm long, 

 0.5 to 1.5 mm wide or sometimes to 3 mm wide in a few forms (fig. 48a). The strongly 

 keeled, acute involucral bracts (fig. 38a) are white, more or less tomentose, 8 to 10 

 mm long, and arranged into 5 distinct vertical ranks. The yellow corollas are 8 to 11 

 mm long and terminate in lobes 1 to 2 mm long. The achenes are densely pubescent. 

 IVhite rubber rabbitbrush is a common and widespread subspecies found in open places in 

 plains and foothills from British Columbia and Montana southward to northwestern 

 Colorado, Utah, Nevada, and eastern California. It is most abundant in the Great Basin 

 area (Hall and Clements 1923) . This subspecies is often found intermixed with ssp. 

 graveolens on foothill ranges, and with ssp. consimilis in valleys and plains (Plummer 

 1977). The striking white forms have potential use as ornamentals. 



Chrysotharmus nauseosus ssp. consimilis (threadleaf rubber rabbitbrush) may reach 

 3 m in height when mature (fig. 49). It has leafy, erect branches covered with a green 

 to yellow-green dense tomentum. The very narrow threadlike (linear-filiform) leaves 

 are less than 1 mm wide and 2.5 to 5 cm long (figs. 48b, 50). They are usually covered 

 with a green to yellow-green tomentum and are somewhat resinous. When crushed, the 

 leaves and twigs emit a strongly disagreeable odor. The involucral bracts are acute. 



Figure 46. — Sheep browsing 

 white rubber rabbitbrush 

 (C. nauseosus ssp. 

 albicaulisj near Ephraim, 

 Sanpete Co., Utah. 



46 



