COMPOSITAE. 327 



Leaves oval to ovate, the lower often petioled. 15. A. 

 leaves abruptly contracted into margined petioles, often enlarged near the 

 base. 16. A. prenanthoides. 



leaves strongly oordate-clasping ; bracts green-tipped. 



17. A. laevis. 

 **Leaves entire or very nearly so. 

 Involucre campanulate, its bracts appressed, green-tipped. 



Stem-leaves oblong, lanceolate or oval-lanceolate. 17. A. laevis. 

 Stem leaves elongated-lanceolate to linear. 18. A. concinnus. 



Involucre hemispheric. 



Bracts in several series, unequal. 19. A. Novi-Belgii. 



Bracts in only 1 or 2 series; leaves linear to lanceolate. 



20. A. longifolius. 



C. Leaves sessile or petioled, not at all clasping or scarcely so. 



Leaves silky, silvery or canescent on both sides, entire. 



21. A. concolor. 

 Leaves neither silky,' silvery nor canescent, often toothed. 



Rays normally purple,' blue, pink or violet; not white. 

 Tips of the involucral bracts strongly squarrose. 



Involucre hemispheric or nearly so ; heads 2.5 cm. broad 

 or more. 

 Bracts of the involucre glandular. 



22. A. speotdbilis. 

 Bracts of the involucre ciliate or glabrous. 



23. A. surculosus. 

 Involucre turbinate; heads 12-18 mm. broad. 



24. A. gracilis. 

 Tips of the involucral bracts appressed or erect. 



Bracts of the involucre coriaceous or herbaceous, oblong, 



linear, lanceolate or spatulate. 25. A. Badula. 

 Bracts of the involucre linear-subulate, membranous, acute. 



26. A. nemoralis. 

 Bays mostly white or nearly so (often pink or purple in Nos. 27, 



28, 29 and 35). 

 Heads solitary at the ends of slender branches. 



27. A. dumosus. 

 Heads paniculate or racemose, 8-20 mm. broad. 



Bracts of the involucre acute or obtusish; plants glabrous 

 or pubescent. 

 Heads paniculate, not in 1-sided racemes. 

 Stem-leaves lanceolate, serrate or entire. 

 Heads 16-20 mm. broad. 



Leaves firm, roughish or rough; rays 



often bluish. 28. A. salicifolius. 

 Leaves thin; smoothish; rays chiefly 

 white. 29. A. pan iculatus. 



Heads 12-16 mm. broad ; stem-leaves narrowly 

 lanceolate. 30. A. Tradescanti. 



Stem-leaves linear-lanceolate to subulate, mostly- 

 entire. 

 Paniculately branched, bushy. 



31. A. eriooides. 

 Simple, or with ascending slender branches. 



32. A. Pringlei. 

 Heads racemose and 1-sided on the branches. 



Stem-leaves oval, oblong, or lanceolate, serrate, or 



chiefly so. 33. A. lateriflorus. 



Stem-leaves linear-lanceolate to linear, nearly en- 

 tire; stem glabrate. 34. A. vimiiieus. 

 Bracts of the involucre, at least the outer, obtuse; plants 

 very rough. 35. A. multifl-orus. 



D. Leaves fleshy, narrow, entire; plants of salt marshes or saline soil. . 



