GENUS 22. THISTLE FAMILY. 381 



Bog species; inflorescence wand-like. 16. S.uliginosa. 



Upland species, the inflorescence various. 

 Heads very short-peduncled. 



Leaves thick, firm in texture, little toothed or entire ; tall species. 



Lower leaves ovate to broadly oval, serrate. 17. 5". speciosa. 



Leaves lanceolate to oblong-lanceolate, entire. 18. 5". rigidiuscula. 



Leaves thin in texture, at least the lower serrate ; low species. 



19. 5". Randii. 

 Heads distinctly slender-peduncled. 



Basal leaves narrowly oblanceolate, 4" wide or less. 20. 5". racemosa. 



Basal leaves broadly oblanceolate or obovate, 6"-i8" wide. 



Heads 4" high; basal leaves sharply serrate. 21. S.Gillmani. 



Heads 3" high ; leaves nearly entire. 22. S. sciaphila. 



*** Heads in a terminal, usually large panicle, secund on its spreading or recurved branches. 



% Plant maritime ; leaves thick, fleshy, entire. 23. S. sempervirens. 



%\ Plants not maritime ; leaves not fleshy. 

 I. Leaves pinnately-veined, not triple-nerved. 



(a) Leaves all entire, thin and glabrous. 24. S. odora. 



(b) Leaves, at least the lower, more or less dentate or serrate. 



t Leaves linear or linear-oblong, i'-2' long, scabrous. 25. 5". tortifolia. 

 tt Leaves broader, lanceolate, oblong, or ovate, z'-io' long. 

 % Stem densely pubescent ; leaves more or less so. 



Leaves not rugose, sparingly dentate or entire. 26. S. fistulosa. 



Leaves rugose-veiny beneath, sharply serrate. 27. S. rugosa. 



t$ Stem glabrous, or merely puberulent above. 



Leaves very rough on the upper surface, serrulate. 28. S. patutu. 



Leaves smooth, or minutely roughened on the upper surface. 

 Racemes few, widely divergent, very slender. 



Lower leaves oblong, coarsely serrate, thin. 29. 5". ulmifolia. 



Lower leaves ovate or lanceolate, rather finely serrate, firm. 30. S. Boottii. 



Racemes numerous, spreading, recurved or ascending. 



Leaves all oblong or oblong-lanceolate, sessile. 31. S.Elliottii. 



At least the lower leaves petioled, lanceolate or ovate-lanceolate. 



Leaves firm, ovate-lanceolate or oblong-lanceolate ; heads about 2" high ; racemes short ; 



rays several. 32. S. neglecta. 



Leaves firm, narrowly lanceolate; heads about 2" high; racemes few, short; rays 1-5. 



33. 5". uniligulata. 

 Leaves firm, lanceolate or oval-lanceolate; heads i l /2 f '-2 l /t" high; racemes numerous, 



slender. 34. 5". juncea. 



Leaves thin, the lower broadly ovate, short-acuminate; heads 2^/2 "-l, 1 /*" high; racemes 

 numerous. 35. S. arguta. 



2. Leaves triple-nerved, i. e., with a pair of lateral veins much stronger than the others. 



Heads small, the involucre only i %" high or less ; stem glabrous, or pubescent. 36. S. canadensis. 

 Heads larger, the involucre ij"-3" high. 

 Stem glabrous. 



Leaves, and involucral bracts thin. 37. S. serotina. 

 Leaves, and involucral bracts firm, somewhat rigid. 



Leaves linear-lanceolate ; achenes glabrous. 38. 5. glaberrima. 



Leaves oblong-lanceolate ; achenes silky-pubescent. 39. S. Shortii. 



Basal leaves oblanceolate, upper bract-like. 40. 5". Ga.tingeri. 

 Stern pubescent or scabrous. 



Leaves lanceolate, sharply serrate or entire, rough above. 41. S. altissima. 

 Leaves oblanceolate, spatulate, oblong, or ovate, the lower crenate. 



Minutely rough-pubescent, grayish ; lower leaves oblanceolate ; heads 2" -3," high. 



42. 6". nemoralis. 



Canescent and pale ; leaves oblong or ovate ; heads 3" high. 43. S. mollis. 



Very scabrous, green, not grayish, nor canescent. 44. S. radula. 



Leaves broadly ovate-oval, sharply serrate, finely pubescent. 45. S. Drummondii. 



**** Heads in a terminal, corymbiform, sometimes thyrsoid cyme, forming a flat-topped inflorescence. 



(Genus OLIGONEURON Small.) 



Leaves ovate, oblong, or oval, mostly rough on both sides. 46. 5. rigida. 

 Leaves lanceolate, linear, oblong, or oblanceolate, glabrous or nearly so. 



Lower leaves oblong-lanceolate, serrulate. 47. S. ohioensis. 

 Leaves all lanceolate or linear, entire. 



Stout; leaves lanceolate, the basal 8'- 12' long. 48. 5". Riddellii. 



Slender ; leaves linear, the basal 4'-s' long. 49. S. Houghtoni. 



