178 GENUS CHRYSOTHAMNUS. 



ECOLOGY AND USES. 



Chrysothamnus teretif alius is essentially like its relative, C. paniculatus, in its ecological 

 behavior. It is more abundant and more widely distributed, and consequently comes 

 in contact with the sagebrush association as well as with the Larrea scrub. It is likewise 

 subclimax in nature, but is found more frequently on gravelly or rocky slopes than in 

 streamways, usually with Hymenodea salsola. 



The strongly resinous nature of its herbage precludes the use of this species as a browse 

 shrub. Its only other possible value lies in the fact that the shrubs contain a small 

 amount of rubber. While this averages only about 2.5 per cent in wild plants, certain 

 individuals have been analyzed that ran as high as 5 per cent (Hall and Goodspeed, 

 Univ. Calif. Publ. Bot. 7:267, 1919; allowance made for moisture determination), and 

 there is no reason to suppose that the strains richest in rubber have as yet been located. 

 The total yield would be considerably increased by any method of mechanical extraction, 

 since much of the resin would come out with the rubber. Such a product would be of 

 low grade, but useful as a rubber substitute if it could be placed on the market in large 

 quantities. The supply of native shrub is not sufficient to be of consequence except in an 

 emergency, such as during war-time, when importations might be excluded, but the 

 improvement of the plants through selection, breeding, and various treatments under field 

 conditions might result in a product and yield so favorable that their cultivation as a 

 rubber crop could be successfully undertaken even in times of peace. For this purpose, 

 however, some of the forms of C. nauseosus are more promising. 



Section II. TYPICI. 

 3. CHRYSOTHAMNUS GRAMINEUS Hall, Muhlenbergia, 2:342, 1916. Plate 25. 



Plant about 3 dm. high, woody at base but scarcely shrubby; twigs probably brittle, 

 stiflBy erect or ascending, greenish-white, striate; leaves lanceolate, acuminate, flat, 

 4 to 6.5 cm. long, 5 to 10 mm. wide, 3- to 5-nerved, some with faint anastomosing veinlets, 

 rigid, the margins scabrous, otherwise glabrous or only minutely granular; heads soUtary, 

 or few in a very open raceme; involucre about 11 mm. high; bracts about 15, the vertical 

 ranks not obvious, oblong, erose at the obtuse summit except the outer slenderly mucro- 

 nate ones, chartaceous and glabrous except the outer which are greenish towards the 

 summit and ciliate; flowers 4 to 5; corolla narrowly funnelform, 12 mm. long, glabrous; 

 lobes 1 to 1.7 mm. long, erect, glabrous; anther-tips attenuate, about 0.6 mm. long; 

 style-branches long-exserted, the appendage over twice as long as the stigmatic portion; 

 achenes nearly terete, 6 mm. or more long, 10-striate, glabrous; pappus nearly equaling 

 the corolla, brownish. 



Known only from the type. Type locality, head of Lee Canon, Charleston Mountains, 

 Clark County, Nevada, altitude 2,450 meters. Collection, tjrpe, August 4, 1913, A. A. 

 Heller 11076 (UC). 



RELATIONSHIPS. 



The position of this exceptionally rare species in the phylogenetic sequence is very 

 uncertain. Its remarkably striate achenes are almost exactly like those of C. vaseyi, 

 but in almost every other detail it is at variance with that species. Except for the 

 number of striae, the achenes closely resemble those of the otherwise very different 

 C. nauseosus leiospermus. The long stylar appendages and the subracemose inflorescence 

 suggest an alliance with C. parryi, but the habit, the glabrous twigs, and especially the 

 glabrous striate achenes, are unlike any member of that group. If it were not for 

 the Pulchelli and C. vaseyi, which seem to relate it to Chrysothamnus because of the striate 

 achenes in all, it might almost as well go into the genus Petradoria (that is, Solidago 

 pumila), which it much resembles in habit, but even there it would be at variance with 



