1012 MISC. PUBLICATION 42 3, U. S. DEPT. OF AGRICULTURE 



S. Humeri from the Chiricahua Mountains (Blumer in 1907), that of 

 S. encelia from the Pinal Mountains (Jones in 1890), that of S. papa- 

 gonius from near " Massacre Camp," between Kuby and the Tucson- 

 Nogales highway (A. and R. E. Nelson 1494) . Colorado, New Mexico, 

 and Arizona. 



One of the most widely distributed and abundant species of Senecio 

 in Arizona. Specimens from the Apache-Verde road, east of Baker 

 Butte (Coville 1043), referred to S. mutabilis Greene by Greenman 

 (see footnote 11, p. 1005, Greenman, vol. 5, p. 49), are not distinguish- 

 able from others referred by him to S. neomexicanus. S. neomexicanus 

 var. griffithsii Greenm. is a form with glabrous achenes (those of the 

 typical form being hirtellous); the type was collected in the Santa 

 Rita Mountains (Griffiths 4212). 



117. CIRSIUM.13 Thistle 



Biennial or perennial herbs, often woolly, with spiny or prickly 

 leaves and involucre ; leaves alternate, toothed or lobed; heads medium 

 or large, discoid, purple, pink, or red, rarely w T hite or greenish yellow; 

 involucre broad, many-seriate, the phyllaries, at least some of them, 

 tipped with spines; receptacle densely bristly; achenes oblong or 

 o bo vate ; pappus of numerous plumose bristles or very narrow paleae, 

 these united at base and deciduous in a ring. 



The Navajo and Hopi Indians are reported to use thistles medici- 

 nally for various disorders. 



Key to the species 



1. Corollas greenish yellow; middle and inner phyllaries arachnoid- villous with 

 long hairs, and with dilated, submembranous, lacerate-fringed tips. 



1. C. PARRYT. 



I. Corollas purple, pink, red, or whitish or, if rarely yellowish (in C. drummondii) , 

 then the involucre not as in C. parryi (2). 

 2. Phyllaries more or less densely and persistently tomentose, the middle ones 



spreading, the outer ones reflexed 3. C. neomexicanum. 



2. Phyllaries glabrous or the margin hispidulous or somewhat arachnoid- 



tomentose, the outer ones not reflexed (3). 



3. Prickles of the involucre very small (less than 2 mm. long), mostly ap- 



pressed (mere cusps rather than prickles) ; phyllaries very numerous, 



with a conspicuous glandular dorsal line; plant glabrate or glabres- 



cent 4. C. wrightii. 



3. Prickles of the phyllaries more than 2 mm. long (4). 



4. Inner phyllaries with elongate, attenuate plane, usually bright red or 

 reddish (rarely purple) tips (5). 

 5. Leaves glabrous or quickly glabrate on both faces (6) . 



6. Spines of the middle phyllaries about 10 mm. long, longer than the 

 body of the phyllaries 5. C. rothrockii. 



6. Spines of the middle phyllaries not more than 5 mm. long, shorter 



than the body of the phyllaries 6. C. bipinnatum. 



5. Leaves persistently tomentose, at least beneath (7) . 



7. Spines of the middle phyllaries 1 to 2 cm. long, stout, yellow- 



ish 7. C. NIDULUM. 



7. Spines of the middle phyllaries shorter, slender (8) . 



8. Corollas bright red or carmine 8. C. arizonicum. 



8. Corollas pink-purple 9. C. pulchellum. 



4. Inner phyllaries with usually more or less dilated and twisted, often 

 erose tips (9). 

 9. Phyllaries stiffly hispidulous -ciliolate (almost serrulate) on the 

 margin 10. C. grahami. 



1 3 Reference: Petrak, F. die nordamerikanischen arten der gattung cirsium. Bot. Centbl. 

 Beihefte 35, Abt. 2: 223-567. 1917. 



