750 CONTEIBUTIONS FROM THE NATIONAL HERBAEIUM. 



None of the bracts dilated at the apex, all with long- 

 attenuate tips, conspicuously arachnoid, in 



many series 3. 0. pallidum. 



At least some of the bracts dilated at the apex, not 

 conspicuously arachnoid, often nearly gla- 

 brous, in few series. 

 Inner bracts conspicuously elongated, with 

 narrow, mostly coriaceous tips; heads 

 small, 2 cm. broad, mostly clustered at 



the ends of the branches 4. 0. inornatum. 



Inner bracts not conspicuously elongated, with 

 broad green tips ; heads large , 3 cm . broad , 



mostly solitary 5. 0. gilense.' 



None of the bracts pectinate-ciliate; flowers variously 

 colored. 

 Bracts not with a dorsal glandular ridge. 



Bracts squarrose, at least the lower reflexed ; largest 



heads 6 to 7 cm. in diameter 6. 0. neomexicanum. 



Bracts not squarrose, all erect or appressed; heads 



all less than 5 cm. in diameter. 



Style produced at the tip only 4 to 6 times its 



diameter above the conspicuous node; 



corollas bright carmine; leaves tomen- 



tose on both sides l- 0. arizonimm. 



Style produced many times its diameter be- 

 yond the inconspicuous node; corollas 

 purplish or wliitish; leaves glabrate, at 

 least above. 

 Inner bracts much elongated, the tips not 

 dilated; heads small, 2 cm. in di- 

 ameter or less 8. C. pulchellum. 



Inner bracts but little elongated, some- 

 what dilated at the tips; heads large 

 or small. 

 Flowers purplish; heads small, about 

 2 cm. in diameter, solitarj^; in- 



\ 



ner bracts Avith purple tips 9. G. wheeleri. ;/ 



Flowers whitish; heads larger, mostly j 



3 to 4 cm. broad, clustered at the 

 ends of the branches; bracts not 



with purple tips iO. 0. coloradense. 



Bracts with a dorsal glandular ridge. 



Bracts scabrous-ciliate, purplish 11. 0. grahami. 



Bracts not scabrous-ciliate, usually not at all pur- 

 plish. 

 Plants glabrate. 



Stems winged below; leaves thin, usually 

 merely dentate with weak spines; 



heads broadly campanulate 12. C. wrightii. 



Stems not winged ; leaves thick, pinnatifid, 

 with stout spines; heads narrowly 

 campanulate 13. 0. calcareum. 



