usually extend beyond the uppermost heads of the inflorescence. Flower heads contain 

 5 to 7 pale yellow disc flowers. The heads are subtended by vertically ranked in- 

 volucral bracts usually with spreading tips. Blooming occurs from July to September. 

 This subspecies occurs on dry hills and mesas associated with sagebrush, pinyon- juniper , 

 and yellow pine vegetational types in Utah, western Wyoming, Colorado, New Mexico, and 

 Nebraska. Type locality is listed as "gravelly hills near 'Hot Springs' of Middle Park, 

 Colo." (Hall and Clements 1923). 



Chvysotharmus parvyi ssp. monocephalus is a low shrub from 0.5 to 3 dm high with 

 rigid, spreading branches. Its viscid, somewhat tomentulose leaves are linear- 

 oblanceolate or spatulate, 1 to 3 cm long, and 1.5 cm or less wide [fig- 39c). The 

 upper leaves usually extend beyond the inflorescence. The flowering heads occur singly 

 or in pairs on the end of short leafy branches. The heads contain 5 or 6 disc flowers 

 and are subtended by obscurely ranked involucral bracts with straight, attenuate tips. 

 This subspecies occurs in the high mountains of western Nevada and eastern California 

 on dry rocky slopes between 3,000 to 3,400 meters (9,800 to 11,200 feet). Its type 

 locality is listed as "summit of Mount Rose, Washoe, Co., Nev." (Hall and Clements 

 1923) . 



Chrysothccrmus parryi ssp. nevadensis (Nevada rabbitbrush) consists of low shrubs 

 with ascending to erect branches up to 6 dm high. The linear to linear-oblanceolate 

 leaves are 1.5 to 4 cm long, 0.5 to 3 mm wide, and sometimes green to resinous, but 

 usually gray-tomentose. The uppermost leaves rarely extend beyond the inflorescence. 

 The flowering heads contain 4 to 6 yellow disc flowers and are subtended by ranked 

 involucral bracts with slender recurved tips. Chrysotharmus parvy-t ssp. nevadensis 

 occurs between 1,300 and 2,700 meters (4,300 and 8,900 feet) in elevation on dry moun- 

 tain sides from eastern California to eastern Nevada, southwestern Utah, and northern 

 Arizona. It is most common along the eastern flank of the Sierra Nevada. Type locality 

 is Mount Davidson, Nevada (Hall and Clements 1923). 



Chvysotharmus parvyi. ssp. pavvyi (Parry rabbitbrush) consists of low shrubs with 

 erect branches 3 dm or more high. The 'uppermost leaves usually extend beyond the in- 

 florescence. Flowering heads contain 10 to 20 disc flowers and are subtended by 

 obscurely ranked involucral bracts with straight attenuate tips. Blooms occur during 

 August and September. Subspecies pavvyi grows in dry plains, valleys, and hillsides 

 in northeastern Nevada, Utah, Wyoming, and Colorado. Type locality is listed as 

 "Rocky Mountains, latitude 39° to 41°" (Hall and Clements 1923). 



There are a few other subspecies of C. pavvyi such as imutus and vulcanicus. 

 These occur outside of or only on the fringe of the Intermountain area and in small 

 numbers (Hall and Clements 1923). 



Chrysothamnus vaseyi (Gray) Greene (Vasey rabbitbrush) 



Vasey rabbitbrush is a low, rounded shrub with ascending to erect branches up to 

 3 dm high. The bark on the young branches is pale green to whitish and glabrous, be- 

 coming brown and fibrous with age. Leaves are linear to linear-oblanceolate, 1 to 2.5 

 cm long, 1 to 3 mm wide, and glabrous. 



Heads contain 5 to 7 disc flowers each and are arranged into small, compact cymes. 

 The obscurely ranked involucral bracts are 5 to 7 mm high, oblong, obtuse to rounded, 

 and all but the innermost have a thickened greenish spot near the apex. The achenes 

 are about 5 mm long, terete, longitudinally 10-striate, and glabrous. Blooming occurs 

 from July to September. 



Hybvidization. --This species has a chromosome number of 2n = 18 (Anderson 1966). 

 The populations of C. vaseyi seem fairly stable with little variation (Hall and Clements 

 1923) . 



53 



