642 CONTEIBUTIOlSrS FROM THE NATIONAL HEEBAEIUM. 



Achenes with retrorsely barbed awns; rays sterile or fertile. 



Rays sterile ; all achenes awned 66. Bidens (p. 703). 



Rays fertile; outer achenes usually not awned. 



67. Heterospermum (p. 705). 

 Achenes, at least those of the disk, never oliconipressed ; involucre various. 

 Rays white; stems prostrate, spreading; bracts of receptacle reduced to 

 awnlike bristles subtending the naked achenes. 



68. EcLiPTA (p. 705). 

 Rays yellow or brown; stems erect; bracts of receptacle concave, loosely 

 subtending the disk achenes. 

 Receptacle conic or columnar. 

 Achenes flattened, distinctly margined or winged. 



69. Ratibida (p. 705). 

 Achenes not flattened, terete or 4-angled, not margined nor winged. 



Achenes terete or nearly so; leaves somewhat glaucous. 



70. Dracopis (p. 706). 

 Achenes 4-angled ; leaves never glaucous. 



Achenes quadrangular-compressed, the apex covered by the base 



of the corolla tube 72. Gymnolomia (p. 707). 



Achenes nearly equally 4-angled, the apex not covered by the 



base of th3 corolla 71. Rudbeckia (p. 707). 



Receptacle from flat to convex. 

 Achenes of the disk not winged nor very flat, when flat not margined 

 nor sharp-edged ; pappus sometimes deciduous, or often wanting. 

 Rays fertile. 



Pai^iJus of conspicuous awns; leaves not 3-lobed. 



74. Wyethia (p. 709). 

 Pappus none in the disk achenes; leaves 3-lobed. 



73. Zaluzania (p. 708). 

 Rays sterile (rarely wanting) . 



Papijus none or a minute ring 72. Gymnolomia (p. 707). 



Pappus of 2 awns or palese. 

 Achenes pubescent; pappus persistent or deciduous. 



75. ViGUiERA (p. 709). 

 Achenes glabrous; pappus deciduous. .76. Helianthus (p. 710). 



Achenes of the disk winged, or flat-compressed and margined, or thin- 

 edged; i^appus persistent. 



Shrub; rays wanting 77. Flotjrensia (p. 711). 



Herbs; rays present. 

 Achenes not winged nor margined. 

 Leaves linear; pappus of 2 palese without intermediate squamel- 



lae 78. Encelia (p. 712). 



Leaves not linear; palese with intermediate squamellae. 



79. Helianthella (p. 712). 

 Achenes winged or margined. 



Only the ray flowers fertile; perennial. 



81. WOOTONELLA (p. 713). 



All the flowers fertile; annuals or perennials. 

 Annual; involucral bracts foliaceous, spreading. 



80. Ximenesia (p. 713). 



Perennials; bracts usually not foliaceous, all, or all except the 



outermost, appressed .82. Verbesina (p. 713). 



