the Intermountain area; others, such as C. panioulatus and C. teretifolius, occur in 

 portions of the Intermountain area but are only minor constituents of the flora. 



Chrysothamnus albidus (Jones) Greene (alkali or white flowered rabbitbrush) 



Alkali rabbitbrush is a much-branched, leafy shrub. It has erect, brittle, gla- 

 brous, very resinous, white-barked branches up to 1 meter high (fig. 39a). The glabrous, 

 filiform leaves are 1.5 to 4 cm long, 0.5 to 2 mm wide, and the margins become revolute. 

 Their surface is covered with small pits and abundant resinous exudate. 



Heads with 4 to 6 white disc flowers each are arranged in small compact cymes. 

 Each head is subtended by approximately 15 glabrous, resinous, involucral bracts. These 

 are 7 to 9 mm long and terminate in attenuate to acuminate, usually curved tips. The 

 pappus is abundant and longer than the corollas. Mature achenes are about 4 mm long 

 and densely covered with long soft hairs. Blooming occurs from August to November. 



Hybridization . --Chrysothamnus albidus has a chromosome number of 2n = 18 (Anderson 

 1966, 1971; Anderson and others 1974). Only diploid individuals have been found in this 

 species. Hybridization between this species and at least C. nauseosus appears possible. 

 Anderson (1970) has obtained seed from C. albidus that produced plants somewhat inter- 

 mediate between the putative parents. 



Perhaps greater alkalinity tolerance could be bred into the more palatable forms 

 of rubber rabbitbrush by crossing them with alkali rabbitbrush. These forms could then 

 be used to increase palatable forage as well as ground cover in sparsely vegetated al- 

 kaline areas. 



Distribution and habitat . --This species is a definite halophyte. It occurs most 

 commonly along the western side of the Great Salt Lake desert, but is also found across 

 Nevada to eastern central California in alkaline soils. Alkali rabbitbrusn may invade 

 strongly alkaline areas as a pioneer plant. In less alkaline flats it may be associated 

 with threadleaf rubber rabbitbrush, giant wildrye, and greasewood. Its type locality 

 is listed as "alkaline soil, Wells, Nevada" (Hall and Clements 1923). 



Use. --This species has value as ground cover on alkaline soils. 



Chrysothamnus depressus Nutt. (dwarf rabbitbrush) 



Dwarf rabbitbrush is a small, irregularly branched, depressed shrub or subshrub 

 3 dm high or less, with numerous short branches arising from decumbent lower stems 

 (fig. 40). The branches are covered with a dense scabrid pubescence. The narrowly 

 oblanceolate to spatulate leaves are 0.7 to 2 cm long, 1 to 4 mm wide, and finely pu- 

 berulent or scabrous like the branches. 



The heads contain 5 disc flowers and are arranged into compact terminal cymes. 

 Involucral bracts have mucronate to attenuate tips, are 10 to 13 mm long, and are ar- 

 ranged into 5 distinct vertical ranks. Achenes are 5 to 5.5 mm long and glabrous or 

 obscurely pubescent toward their apex. The soft brownish-white pappus is slightly 

 longer than the corolla. Blooming occurs from May to October. 



Hybridization. — Chrysothamnus depressus has a chromosome number of 2n = 18 

 (Anderson 1966). It is not known to hybridize with any other rabbitbrush. 



Distribution and habitat .- -This species occurs on dry plains, hills, and rocky 

 mountain slopes from 1,000 to 2,100 meters in elevation (3,300 to 6,900 feet) scattered 

 over western Colorado, New Mexico, Utah, Nevada, and southeastern California. 



39 



