882 MISC. PUBLICATION 42 3, U. S. DEPT. OF AGRICULTURE 



1. Receptacle naked or rarely fimbrillate, not paleaceous (30). 

 30. Involucre and leaves with translucent oil glands (31). 



31. Phyllaries 1-seriate, united almost to the apex into a toothed cup or 



tube; pappus of 5 or 6 unequal paleae 102. Tagetes. 



31. Phyllaries more or less 2-seriate, or else quite free; pappus otherwise (32). 

 32. Leaves without stiff spreading bristles at base; phyllaries more or less 

 2-seriate, often partly united, often with bractlets at base. 



103. Dyssodia. 

 32. Leaves with a few stiff spreading bristles at base; phyllaries 1-seriate, 



free, without bractlets at base 105. Pectis. 



30. Involucre and leaves without translucent oil glands (33). 

 33. Rays white, pink, blue, or purple (34). 



34. Achenes compressed, 2-edged or 2-nerved (35). 



35. Pappus, at least in the disk flowers, of several or many paleae or 

 flattened bristles; phyllaries with scarious margin and tip. 



26. Townsendia. 

 35. Pappus of only 1 or 2 bristlelike awns, or a crown of squamellae, 

 or both; phyllaries not scarious-margined (36). 

 36. Pappus of a minute setulose crown only; leaves entire, alternate. 



23. AcHAETOGERON. 



36. Pappus of 1 or 2 weak awns, with or without a crown of squamel- 

 lae; leaves usually toothed, lobed, or dissected, at least the 

 lower ones opposite (37). 

 37. Pappus of 1 or 2 awns and a crown of squamellae; achenes 



usually callous-margined and ciliate 83. Perityle. 



37. Pappus of 1 or 2 awns, without squamellae; achenes not callous- 

 margined, not ciliate 84. Laphamia. 



34. Achenes more or less thickened, 4- or 5-angled (38). 

 38. Pappus a low dissected or ciliolate crown only (39). 



39. Leaves toothed to pinnatifid, or the upper ones entire; phyllaries 

 green-centered, scarious-margined 21. Aphanostephus. 



39. Leaves entire; phyllaries whitish, thick, chartaceous, with a 



scarious margin and a green tip 22. Greenella. 



38. Pappus of distinct awns or paleae, sometimes also with a low crown 

 (40). 



40. Phyllaries with a conspicuous scarious whitish or yellowish margin 



and tip; plants perennial or biennial 90. Hymenopappus. 



40. Phyllaries without a conspicuous scarious margin and tip; plants 

 annual (41). 

 41. Herbage hispid-pilose; upper leaves subtending the heads. 



25. Monoptilon. 

 41. Herbage woolly; heads not subtended by the upper leaves. 



93. Eriophyllum. 

 33. Rays yellow (42). 



42. Phyllaries distinctly graduated, in several series (43). 



43. Pappus of 2 to 8 slender caducous awns 10. Grindelia. 



43. Pappus otherwise (44). 



44. Annual herbs; rays 12 to 50 9. Xanthocephalum. 



44. Perennial herbs or shrubs; rays 12 or fewer, except in genus 

 Acamptopappus (45). 

 45. Heads comparatively large, solitary; pappus of numerous, 

 narrowly linear awns and bristles, several-seriate. 



14. Acamptopappus. 

 45. Heads small or very small, clustered (46). 



46. Disk achenes with a pappus of several straight paleae or 

 squamellae in a single series; involucre not compressed; 



leaves chiefly linear 12. Gutierrezia. 



46. Disk achenes with a pappus of numerous more or less twisted, 

 flattened bristles or narrow paleae; involucre compressed; 



leaves obovate or elliptic 13. Amphipappus. 



42. Phyllaries equal or subequal or in 2 unequal series, not distinctly 

 graduated (47). 

 47. Rays persistent on the achenes, becoming papery (48). 



48. Rays 3 to 5, about as wide as long; achenes linear, slightly angled, 

 essentially glabrous 81. Psilostrophe. 



