316 FLORA OF PHILADELPHIA. 



Bracts of the involucre searious, mostly white or pink; plants 

 woolly. 

 Plants dioecious or polygamo-dioecious. 



Pappus-bristles of staminate flowers thickened above. 



24. Antennaria. 

 Pappus-bristles not thickened; stem leafy. 



25. Anaphalis. 

 Plants not dioecious; flowers all fertile. 26. Gnaphalium. 



Heads large; ray-flowers yellow. 27. Inula. 



Tribe 5. HELIANTHEAE. 



A. Disk-flowers perfect but sterile. 



Achenes thick, short, not flattened; pappus none. 28. Polymnia. 

 Acbenes flattened. 



Ray-flowers in 2 or 3 series; achenes falling away free. 



29. Silphium. 

 Bay-flowers in 1 series; achenes adnate to 2 or 3 scales of the re- 

 ceptacle, falling away with them. 30. Chrysogonum. 



B. Disk-flowers fertile. 



Bay-flowers persistent upon the achenes. 31. Heliopsis. 



Bay-flowers deciduous or none. 



Pappus a cup, or crown, or of a few teeth, awns, or bristles. 



Achenes, at least those of disk-flowers, not compressed (except 

 in Verbesina) ; scales of the receptacle mostly concave, 

 or clasping. 

 Scales of the receptacle small; awn-like or bristle-like; 



rays white, short. 32. Eclipta. 



Scales of the receptacle broad, larger. 



Beceptacle conic or columnar. 33. RudbecMa. 

 Beceptacle flat or merely convex. 



Achenes not much flattened, not winged nor mar- 

 gined. 34. .Helianthus. 

 Achenes of disk-flowers flattened and margined, 

 or winged. 35. Verbesina. 

 Achenes very flat ; scales of the receptacle flat, or but slightly 

 concave. 

 Pappus of 2 short teeth or 'awns, or a mere border, or 



none. 36. Coreopsis. 



Pappus of 2-6 awns or teeth, upwardly or downwardly 

 barbed or hispid. 37. Bidens. 



Pappus of numerous scales. 38. Galinsoga. 



Tribe 6. HELENIEAE. 

 Tribe 7. ANTHEMIDEAE. 



39. Helenium. 



Beceptacle chaffy. 



Achenes flattened; involucre obovoid to campanulate ; heads small. 



40. Achillea. 

 Achenes terete; involucre hemispheric; heads large. 



41. Anthemis. 

 Beceptacle not chaffy, naked, or sometimes hairy. 



1. Bay-flowers usually present, sometimes wanting; rays large. 



Beceptacle flat to hemispheric; bracts of the involucre in several 



series. 42. Chrysanthemum. 



Beceptacle conic to ovoid; bracts in few series; rays white or none. 



43. Matricaria. 



2. Bay-flowers none; heads small. 



Heads corymbed; pappus a short crown; flowers yellow. 



44. Tanacetum. 



