Genus 3I-] THISTLE FAMILY. 355 



(b) Leaves thick, firm, rough. 

 Heads 6"-8" high; inflorescence forking. 4. A. /ureal us. 



Heads 4" -5" high; inflorescence paniculate or glomerate. 



Leaves acute, or short-acuminate, pilose beneath; inflorescence glomerate. 5. A. glomeratus. 

 Leaves long-acuminate, not pilose beneath; inflorescence open-paniculate. 6. A. Claytoni. 

 t t Involucre cylindrie, its bracts tapering to an obtuse apex; basal leaves large, tufted. 

 Bracts of the involucre pale, scarious, usually without herbaceous tips. 7. A. curvescens. 



Bracts of the involucre broader, with herbaceous tips. 8. A. Schreberi. 



\ \ Rays violet, usually 3-toothed; plants glandular, 

 f Predominant glands large, capitate; leaves thick, coarse, heavy. 

 Sinus broad; glands chiefly confined to the inflorescence; plant usually harsh. 9. A. macrophyllus. 

 Sinus narrow; glands abundant on the leaves and stem; growing plant clammy. 10. A. roscidus. 

 f f Predominant glands minute, scarcely capitate; leaves usually thin. 

 (a) Inflorescence rather regular, flat, or convex-topped; plants usually less than 2^ tall. 

 Sinus broad, shallow. 



Broader leaves orbicular-cordate, their teeth and the inflorescence-leaves inconspicuous. 



11. A. ianthinus. 

 Broader leaves reniform, sharply incised; some inflorescence-leaves conspicuous. 



12. A. violaris. 

 Sinus rather deep and narrow; broader leaves ovate-cordate, sharply serrate. 13. A. multiformis. 

 (b) Inflorescence very irregular, paniculate-corymbose; plants often 4-5 high; broader leaves 



large, cordate, acute. 14. A. nobilis. 



X- -Sf Rays blue or purple; plants not glandular. 

 t Bracts of the involucre spreading or recurved; rays 30-45. 15. A. anomalus. 

 t t Bracts of the involucre appressed, or erect; rays 8-20. 

 (a) Leaves all entire, or nearly so, thick, or firm. 

 Leaves nearly or quite glabrous above. 16. A. Shortii. 



Leaves rough-puberulent on both sides, the upper bract-like. 17. A. azureus. 



(b) Leaves nearly all sharply serrate, thin. 

 Heads 2" -3" high, numerous; bracts obtuse or obtusish. 



Leaves rough; petioles not wing-margined; bracts appressed. 18. A. cordifolius. 



Leaves smooth, or nearly so; petioles, or some of them, wing-margined. 19. A. Lowrieanus. 

 Heads 4"-5" high, usually few; bracts acute or acuminate. 20. A. Lindleyanus. 



Heads $"-5" high, numerous; bracts acute or acuminate. 



Stem densely and finely pubescent. 21. A. Drummondii. 



Stem glabrous or nearly so; bract-tips spreading. 22. A. sagittifolius. 



2. Stem leaves, or some 0/ them, cordate-clasping ; plant rough when dry. 



___ jfcgf- 23. A. undulatus. 



B. No cordate and petioled leaves; those of the stem, or some of them, with more or less cordate or auricled 



clasping bases. 



1. Stem rough, or hirsute-pubescent. 



X- Leaves entire, oblong, linear, or lanceolate. 



\ Heads 1/-2' broad; leaves sessile, strongly cordate-clasping. 



t Stem rough; leaves oblong to lanceolate; involucre turbinate. 



Leaves thick, firm, very rough, oblong to oval. 24. A. patens. 



Leaves thin, roughish, oblong-lanceolate. 25. A. phlogifolius. 



t t Stem hirsute; leaves lanceolate; involucre hemispheric. 26. A. Novae- Angliae. 

 ji Heads 'A'-i' broad; leaves but slightly clasping. 

 Involucre hemispheric, its bracts glandular. 27. A. oblongifolius. 



Involucre turbinate, its bracts hispid. 28. A. amelhystinus. 



Sfr -K- Leaves, at least the lower, serrate. 

 Stems usually pilose; bracts very glandular. 29. A. major. 



Stem hispid-pubescent; bracts glabrous, or ciliate. 30. A. puniceus^ 



2. Stem glabrous, or only sparingly pubescent above. 

 Xr Leaves sharply serrate. 

 ? Leaves tapering to the base. 

 Outer bracts of the involucre foliaceous. 31. A. tardijlorus. 



Bracts of the involucre narrow, not foliaceous. 



Leaves lanceolate, to oblong-lanceolate, sessile. 30. A. puniceus. 



Leaves oval to ovate, the lower often petioled. 32. A. patulus. 



j/ \ Leaves abruptly contracted into margined petioles, often enlarged near the base. 



23. A. prenanlhoides. 

 \\\ Leaves strongly cordate-clasping; bracts green-tipped. 34. A.laevis. 

 %r vc Leaves entire, or very nearly so. 

 Involucre campanulate, its bracts appressed, green-tipped, 

 t Bracts of the involucre with rhomboid green tips. 

 Stem leaves oblong, lanceolate, or oval-lanceolate. 34. A. laevis. 



Stem leaves elongated-lanceolate. 35. A. concinnus. 



f t Bracts of the involucre linear, the tips narrower, lanceolate; stem leaves linear or narrowly 



lanceolate. 36. A. purpuratus. 



iJ \ Involucre hemispheric. 

 t Bracts of the involucre narrow, not foliaceous. 

 (a) Bracts in several series unequal. 

 Bracts linear-subulate ; leaves narrowly linear. 37. A.junceus. 



Bracts lanceolate, linear, or spatulate; leaves lanceolate to linear. 



Western dry soil plant, i-2 tall; leaves i'-3' long. 38. A. adscendens. 



Eastern swamp plant, 2-5 tall; leaves 2'-6' long. 39. A. Novi-Belgii. 



(b) Bracts in only 1 or 2 series; leaves linear to lanceolate. 40. A. longifolius. 

 t t Bracts of the involucre green, foliaceous; western. 41. A.foliaceus. 



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

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



Heads corymbose-paniculate; bracts oblong; achenes glabrous. 42. A. sericeus. 



Heads in a narrow raceme; bracts linear; achenes silky. 43. A. concolor. 



