125. CoMPOsiTAE 235 



28. Bracts of the in\olucre pectinate, or tipped with a 



rigid spine 57. Centaurea 



28. Bracts neither pectinate nor with a ri-^id spine. 



29. Bracts with hooked tips: ( oarse biennial weeds 

 with large ovate chiefly basal leaves; heads 

 globose ; flowers purple ( rarely white ) ; recepta- 

 cle l)ristly 52. Arctium 



29. Bracts not hooked; receptacle not bristly. 



30. Flowers yellow; bracts in 1 series 51. Senecio 



30. Flowers not yellow; bracts imbricated in 2- 

 several series. 

 31. Pappus-bristles plumose or barbellate; heads 

 in long racemes or spikes; leaves narrow, 



entire, rigid 10. Liatris 



31. Pappus-bristles not plumose. 



32. Pappus (in our species) double, the 

 outer bristles short; heads many- 

 flowered, in corymbose cymes; bracts 



imbricated in several series 



5. Vernonia 



32. Pappus-bristles approximately the same 

 length, not in two series. 

 33. Heads 2- to 5-flowered, aggregated 

 into dense clusters subtended by 

 foliaceous bracts: flowers all per- 

 fect and alike; bracts eight 



6. Elephantopus 



33. Heads many-flowered, corymbose; 

 flowers of 2 kinds in the same 

 head ; bracts imbricated ; plants 



camphor-scented 21. Pluchea 



1. Pappus not of capillary bristles, either of rigid awns, small chaflfy scales, or 

 reduced to a mere crown, or entirely lacking. 

 34. Heads radiate. 

 35. Rays yellow. 



36. Pappus of 2-several awns or bristles, these sometimes deciduous. 

 37. Bracts of the involucre with recurved or hooked tips, often 



gummy; leaves alternate, sessile, dentate 11. Grindelia 



37. Bracts not hooked or gummy. 



38. Pappus of 2 smooth awns 35. Verbesina 



38. Pappus of 2-several barbed awns. 



39. Leaves alternate, linear 12. Gutierrezia 



39. Leaves opposite or whorled, not linear 38. Bidens 



36. Pappus none, or of few short teeth or scales. 

 40. Leaves all or mostly opposite or whorled. 



41. Achenes thick, not at all. or scarcely flattened. 



42. Leaves thin, deeply angulate-lobed or lyrate- 



pinnatifid 25. Polymnin 



42. Leaves thick, entire or serrate; rays conspicuous. 



43. Bracts obtuse; ray-flowers pistillate, fertile, papery 



and persistent on the achene 28. Heliopsis 



43. Bracts acute or acuminate; ray-flowers neuter, 



deciduous 34. Helianthus 



