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



The fragrant-bitterweed (A. odorata), and pingiie or "pingwing" 

 (A. richardsoni), are toxic to livestock, especially to sheep, but are 

 eaten only when other forage is scarce. These plants tend to increase 

 on over-grazed ranges. The latex of some of the species contains 

 rubber and A. richardsoni var. floribunda is known as Colorado 

 rubber-plant. The Hopi are reported to make a stimulating drink 

 from A. acaulis var. arizonica and to apply the plant locally in allevi- 

 ating pain, especially in pregnancy. The bark of the roots of A. 

 richardsoni is used as a substitute for chewing gum by Indians in 

 New Mexico. Arizona's larger-headed species are handsome and A. 

 acaulis is cultivated in Europe as an ornamental. 



Key to the species 



1. Heads solitary (rarely 2 or 3), long-peduncled, on naked scapes or sparsely 

 leafy stems; leaves entire or 3-parted (2). 

 2. Involucre densely and loosely pilose-tomentose with matted h,airs; basal 

 leaves narrowly linear, entire or 3-parted; stem about 10 to 20 cm. 

 high, sparsely leafy; pappus of about 5 lance-attenuate paleae. 



1. A. BRANDEGEI. 



2. Involucre not densely and loosely pilose-tomentose, although sometimes 



silky-villous (3). 



3. Phyllaries lanceolate, the outer ones subherbaceous, acuminate, the 



inner ones attenuate, indurate, stiff; leaves not punctate, the basal 



leaves narrowly linear, entire or sometimes 3-lobed; stem 20 to 40 cm. 



high, sparsely leafy; pappus of 10 lance-attenuate paleae. 



2. A. BIGELOVII. 



3. Phyllaries mostly elliptic or oblong, obtuse or merely acute; leaves con- 

 spicuously impressed-punctate (4). 

 4. Plant strictly scapose, the leaves all basal; scapes always simple and 

 1-headed; basal leaves narrowly oblanceolate, sparsely or rather 



densely silky-pubescent 3. A. acaulis. 



4. Plants with the stems sparsely leafy, at least below; stems often few- 

 branched, 1- to 3-headed (5). 

 5. Leaves glabrous or rather sparsely silky-pilose, especially beneath. 



4. A. LEPTOCLADA. 



5. Leaves densely silvery -silky with appressed hairs__ 5. A. argentea. 

 1. Heads several or many, cymose or cymose-panicled; stems very leafy; leaves 

 almost always deeply pinnatifid (6). 

 6. Stems several or numerous from a perennial multicipital caudex, con- 

 spicuously long-villous or woolly at base among the petiole-bases of the 



lowest leaves 6. A. richardsoni. 



6. Stems solitary or few from an annual, biennial, or perennial root or caudex, 

 not long-villous or woolly at base (7) . 

 7. Plant annual, usually branching almost from the base__ 7. A. odorata. 

 7. Plant biennial or perennial, usually branching only in the inflorescence (8). 

 8. Plant subsericeous-canescent; leaves entire or 3-cleft, the blades or 

 their lobes relatively broad, 1.5 to 4 mm. wide-- 8. A. subintegra. 

 8. Plant green or, if slightly canescent, then the leaves or their lobes much 

 narrower (9). 

 9. Leaves either entire or divided into 3 to 5 lobes, the blades or their 

 lobes relatively broad, mostly 2 to 5 mm. wide (10). 

 10. Heads usually few (3 to 10 per stem, rarely more) and com- 

 paratively large (the disk 10 to 18 mm. thick), on more or less 

 elongate peduncles distinctly surpassing the leaves; leaves 

 divided into 3 or 5 lobes, or the lowest sometimes entire. 



9. A. lemmoni. 



10. Heads numerous and small (disk 5 to 10 mm. thick), in close 



rounded or flattish cymes or cymose panicles, on peduncles 



scarcely or not surpassing the leaves; leaves entire or the middle 



ones divided into 3 or 5 lobes 10. A. rusbyi. 



