250 American Midland Naturalist Monograph No. 7 



11. Leaves not clasping. 



19. Leaves densely appressed silveiy-silky on both sides; 

 rays violet; sandy soil, often in open woods, local. 



Sept. -Oct. Silky Aster. A. sericeus Vent. 



19. Leaves not silvery-silky. 



20. Heads not in flat-topped corymbs. 



21. Involucre conspicuously tin-binate, 8-12 mm high, 

 the bracts linear-spatulate, obtuse, appressed, 

 rounded on the back, imbricated in 5 or 6 

 series, green only near the apex; rays violet- 

 blue; prairie soil, local, chiefly in the south- 

 ern part of the state, but extending northward 

 to Christian and Fulton counties. Sept. -Oct. 



A. turbinellus Lindl. 



21. Involucre hemispherical to campanulate; bracts 

 not roimded on the back. 

 22. Involucres 3-7 mm high. 



23. Bracts of the involucres (and uppermost 



leaves) minutely spinulose-tipped or 



evidently bristly ciliate; heads small, 



usually numerous, paniculate. 



24. Stems pilose to glabrous; rays white. 



25. Involucres 4-8 mm high. 



26. Stem pilose ; roadsides, fields, 

 open woods, abundant 

 throughout 111.; a plant of 

 disturbed soil, hence much 

 more common in recent years. 



Aug.-Oct. .- A. pilosus Willd. 



26. Stem and leaves glabrous; dry 

 sandy ridges, shore of Lake 



Michigan. Aug.-Oct 



A. pringlei (A.Gray) Britt. 



25. Involucres 3-4 mm high; disk 

 florets 6-12; praiiies and open 

 woods in the northern half of 111. 



Aug.-Oct A. parviceps 



(Burgess) Mack. & Bush 

 24. Stems and branches copiously short- 

 hirsute; bracts bristly ciliate; leaves 

 linear, entire, 2-5 mm wide, hireu- 

 tulous, cuspidate; heads nimierous; 

 involucres 4-5 mm high. 

 27. Bracts acute, ascending, rays light 

 blue or pink, about 5 mm long; 

 stem pubescent ; moist ground, 

 rare; Champaign, Cook, Mc- 



