598 



COMPOSITAE 



Internodes of the stem prominently 



angled below the leaves. 13. 5. patula. 



Internodes of the stem essentially 

 terete. 

 Stem pubescent, rarely only in 

 lines. 

 Leaves glabrous and essen- 

 tially entire. 14. 5. odora. 

 Leaves pubescent. 



Leaves not rugose veiny. 15. S. fistulosa. 

 Leaves rugose veiny and 



serrate. 16. 5. rugosa. 



Stem glabrous, at least below the 

 inflorescence. 

 Branches of the inflorescence 

 pubescent. 

 Involucre cylindric, few- 

 flowered. 17. 5. ulmifolia. 

 Involucre campanulate, 

 many-flowered. 

 Branches of the in- 

 florescence short 

 and approximate, 

 forming a com- 

 pact pyramidal 

 panicle. 18. 5. Elliottii. 

 Branches of the in- 

 florescence elon- 

 gate and remote. 19. 5. arguta. 

 Branches of the inflorescence 

 glabrous. 

 Involucre 5 mm. high 



or less. 20. S. juncea. 



Involucre mostly over 5 

 mm. high. 

 Rays several ; leaves 

 broadly lanceo- 

 late. 21. 5. neglecta. 

 Rays 1-5; leaves 

 narrowly lanceo- 

 late. 22. 5. uniligulala. 

 Leaf blades markedly 3-ribbed. 



Heads small; involucre 2.5 mm. high or 



less; stem glabrous or pubescent. 23. S. canadensis. 



Heads larger; involucre 3-6 mm. high. 



Stem glabrous. 24. 5. serotina. 



Stem pubescent or scabrous. 



Leaves lanceolate, sharply ser- 

 rate to entire. 25. 5. altissima. 

 Leaves oblanceolate to oblong, 



the lower crenate. 26. S. nemoralis. 



Heads in a terminal corymb; involucral bracts ribbed. 27. 5. rigida. 



