Figure 47. — A white rubber' 

 rabbi tbrush (C. nau- 

 seosus ssp. albicaulisj 

 growing near Fountain 

 Green^ Sanpete Co.^ 

 Utah, The stake is 

 1. 5 m tall. 



glabrous, and keeled and are arranged in fairly distinct vertical rows. The bracts 

 are 6.5 to 8.5 mm long. The corollas are 7 to 9.5 mm long, with glabrous lobes 1 to 

 2.5 mm long. The achenes are densely pubescent, suggesting that this subspecies may 

 be a connecting link between rubber rabbitbrush and low rabbitbrush. 



Chromatograms of threadleaf rubber rabbitbrush were found to be strikingly similar 

 to those of the C. visaidiflorus complex (Hanks and others 1975) . Subspecies 

 Qonsimilis is most common in alkaline valleys and plains of the Great Basin where it 

 is often associated with various saltbushes. In less alkaline areas oonsimilis inter- 

 mixes with ssp. albioaulis and graveolens . Oonsimilis also occurs in alkaline soil 

 outside the Great Basin from western Wyoming, Colorado, and New Mexico to northeastern 

 Oregon and eastern California. A large ecotype that occurs principally in the western 

 part of its range was formerly recognized as a separate subspecies, viridulus . Another 

 subspecies, pinifolius , has also been reduced to synonymy with oonsimilis. Plants 

 formerly referred to as pinifolius grow in southern Colorado and New Mexico. Thread- 

 leaf rubber rabbitbrush is one of the least palatable of the C. nauseosus subspecies. 

 It may therefore have value in revegetating disturbed sites such as roadcuts where 

 attraction of browsing animals is not desired. This subspecies helps control erosion 

 on open alkaline soils by providing ground cover and soil stabilization. 



Chry sotharmus nauseosus ssp. graveolens (green rubber rabbitbrush) ranges from 6 

 to 15 dm high when mature (fig. 51). Its leafy, erect branches are yellow-green to 

 green or sometimes gray-green and are covered with a compact tomentum. The linear 

 leaves are 1 to 3 mm wide, 4 to 6 cm long, and only slightly pubescent (fig. 48c). 

 The involucral bracts are 6 to 8 mm long, glabrous at least on their backs, acute, 

 keeled, and arranged in vertical rows. The yellow corollas are 7 to 9 mm long with 

 lobes 0.5 to 1.5 mm long. Achenes are densely pubescent. Green rubber rabbitbrush is 

 widespread and sporadic from North Dakota to Idaho and southward to western Texas, 

 New Mexico, and Arizona. It is most common on well-drained foothills (fig. 52), but 

 also extends up into the mountains and down into valleys and plains where it is often 

 found intermixed with ssp. oonsimilis. Green rubber rabbitbrush is generally less 

 palatable than the white or grey subspecies, albioaulis and salicif olius . Nevertheless, 

 some forms of this subspecies have been found which are utilized to a moderate degree 

 by livestock and mule deer. 



Chry sotharmus nauseosus ssp. salicif olius (mountain rubber rabbitbrush) is a shrub 

 from 3 to 20 dm high (fig. 53). Its ascending to erect twigs are very leafy and are 



47 



