CARDUACEAE 



1191 



Involucres cylindric-turbinate or cylindric- 



campanulate, about 2 mm. thick. 

 Bracts of the involucre obtuse : stems 

 and leaves somewhat shaggy-pubes- 

 cent : leaf-bladesappressed-serrate. 42. S. Earlei. 

 Bracts of the involucre acute : stems and 

 leaves scabrous- pubescent : leaf- 

 blades sharply serrate. 43. S. pendula. 

 Involucres cam panulate, about 3 mm. thick. 51. S. strigosa. 

 Leaf-blades rugose-veiny. 



Leaf- blades decidedly acute or acuminate, mostly 



over thrice as long as broad. 44. S, rugosa. 



Leaf-blades obtuse or acutish, mostly about twice 



as long as broad. 45. S. celtidifolia. 



f f Stem glabrous, at least below the inflorescence. 

 Branches of the inflorescence pubescent. 

 Involucre cylindric, few-flowered. 

 Involucre not spirally twisted. 



Inner bractsof the involucre 3 mm. long, obtuse. 46. S.ulmtfolia. 

 Inner bracts of the involucre 4 mm. long, acute. 47. S. microphylla. 

 Involucre spirally twisted. 48. S. Helleri. 



Involucre cam panulate, many-flowered. 



Leaf-blades relatively thick, singly serrate except 



In robust plants of S. strigosa. 

 Branches of the inflorescence short and ap- 

 proximate, forming a compact pyramidal 

 panicle. 49. S. Elliottii. 



Branches of the inflorescence elongated and 

 remote, when abbreviated, the head-clus- 

 ters in an elongated interrupted thyrsus. 

 Involucre 3-4 mm. high. 



Leaf-blades glabrous, smooth. 50. S. Boottii. 



Leaf-blades strigose. scabrous. 51. S. strigosa. 



Involucre 5-6 mm. high. 



Cauline leaves, or some of them, with 

 finely and closely toothed blades : 

 leaves of the inflorescence-branches 

 linear to linear-lanceolate. 52. S. Yadkinensis. 



Cauline leaves, or some of them, with 

 coarsely or remotely toothed blades: 

 leaves of the inflorescence-branches 

 elliptic to cuneate. 53. S. Ludoviciana. 



Leaf-blades relatively thin, mainly doubly ser- 

 rate with spreading teeth. 



Involucres 3.5-4.5 mm. high. 2-2.5 mm. thick. 54. S. arguta. 

 Involucres 5-6 mm. high, 3-4 mm. thick. 55. S. Vaseyi. 



Branches of the inflorescence glabrous. 

 Involucre less than 5 mm. high. 



Bracts of the involucre obtuse : involucre cam- 



panulate. 

 Inner bracts of the involucre 0.5 mm. wide : 



basal leaves with serrate blades. 56. S. juncea. 



Inner bracts of the involucre 1 mm. wide : 



basal leaves with crenate blades. 57. S. gradllima. 



Bractsof the involucre acute: involucre cylindric. 58. S. delicatula. 

 Involucre over 5 mm. high. 



Lower leaves with romotely toothed blades: 



achenes 2.5-3 mm. long. 59. S. austrina. 



Lower leaves with closely toothed blades : achenes 



1.5-2 mm. long. 60. S. neglecta. 



* * Leaf-blades manifestly 3-ribbed. 

 Stem glabrous. 



Cauline leaves abruptly smaller from near the base of the stem : 



leaves erect or appressed : achenes glabrous. 61. S. Gattingeri. 



Cauline leaves not abruptly smaller above the base of the stem : 



achenes pubescent. 

 Branches of the inflorescence glabrous. 



Involucres campanulate : species trans- Alleghenian. 62. S. Missouriensis. 



Involucres cylindric-campanulate : species Carolinian. 63. S. pinetorum. 

 Branches of the inflorescence pubescent. 64. S. serotina. 



Stem pubescent, rarely minutely so, or only in lines. 



Cauline leaves with relatively long blades, acuminate or at- 

 tenuate. 



Involucres 5-6 mm. high. 65. S. Shortii. 



Involucres 2-4 mm. high. 



Cauline leaves with blades of a linear type. 

 Involucre about 4 mm. high. 



Involucre turbinate-carnpanulate : leaf-blades long- 

 attenuate. 66. S. Nashii. 

 Involucre broadly campanulate : leaf-blades acu- 

 minate. 67. S. Leavenworthii. 

 Involucres 2-3 mm. high. 68. S. rupestris. 

 Cauline leaves with blades of a lanceolate or oblong-lan- 

 ceolate type. 69. S. Canadensis. 

 Cauline leaves with relatively short blades, obtuse or merely 



acute. 

 Blades of the upper leaves narrow, or if relatively broad closely sessile. 



