908 MISC. PUBLICATION 42 3, U. S. DEPT. OF AGRICULTURE 



in saline soil, June to September. Colorado to Texas, Arizona, and 

 northern Mexico. 



Jimmyweed, rayless-goldenrod. The plant often occupies over- 

 grazed range land and is a common roadside weed in the irrigated 

 districts. This, and doubtless some of the closely related species, are 

 generally unpalatable, but when eaten in quantity by cattle cause 

 the disease known as "milk sickness/' or " trembles," which is trans- 

 missible through the milk to human beings. 



19. Aplopappus drummondii (Torr. and Gray) Blake in Standi., 

 Contrib. U. S. Natl. Herbarium 23: 1491. 1926. 



Linosyris drummondii Torr. and Gray, Fl. North Amer. 2: 233. 



1842. 

 Isocoma drummondii Greene, Erythea 2: 111. 1894. 

 Isocoma rusbyi Greene, Leaflets 1: 170. 1906. 



Apache, Navajo, and Coconino Counties, about 5,000 feet, July to 

 November, type of Isocoma rusbyi from Holbrook (Rusby in 1883). 

 Texas to northern Arizona, and northeastern Mexico. 



19. CHRYSOTHAMNUS. 63 Rabbitbrush 



Shrubs; leaves alternate, linear to linear-filiform, sometimes dotted 

 with impressed glands; heads small or medium-sized, discoid, yellow, 

 4- to 7-flowered, usually panicled; involucre several-seriate, graduated, 

 the phyllaries chartaceous, sometimes herbaceous-tipped, in more or 

 less definite vertical ranks; achenes pubescent or glabrous; pappus of 

 numerous capillary bristles. 



The latex of several species (C. nauseosus, C. paniculatus, C. viscidi- 

 florus), contains rubber of fair quality, that of C. nauseosus being 

 reported to yield 2.8 percent on the average and as much as 6.5 percent 

 in selected individual plants. It has not proved practicable, as yet, 

 to utilize this source of rubber commercially, notwithstanding the 

 great abundance of the plants. The rubber content is reported to be 

 highest in plants growing in saline soil. Several species are browsed 

 to a limited extent, but the genus as a whole is of small forage value. 

 The plants tend to increase on overgrazed land at the expense of more 

 valuable species. Rabbitbrushes are used by the Hopi as one of the 

 "kiva" fuels, and for making windbreaks, arrows, and wickerwork. A 

 yellow dye is obtained from the flowers and a green dye from the inner 

 bark. 



Key to the species 



1. Leaves conspicuously punctate with impressed glands, terete or slightly flat- 

 tened; plants glabrous throughout (2). 

 2. Phyllaries with the midrib often glandular-thickened for most of its length, 

 but without a roundish terminal gland 1. C. paniculatus. 



2. Phyllaries with a large roundish terminal gland 2. C. teretifolius. 



1. Leaves not punctate with impressed glands (3) . 



3. Stems covered with a dense, often matted tomentum (4). 



4. Heads in a leafy spikelike panicle, or in racemelike clusters; outer phyllaries 



acuminate, herbaceous-tipped 7. C. parryi. 



4. Heads cymose, terminal; phyllaries obtuse to acute, not herbaceous-tipped. 



8. C. NAUSEOSUS. 



w Reference: Hall, H. M. and Clements, F. E. the phylogenetic method in taxonomy, the 



NORTH AMERICAN SPECIES OF ARTEMISIA, CHRYSOTHAMNUS, AND ATRIPLEX. Carnegie Inst. 



Wash. Pub. 326: 157-324. 1923. 



