THISTLE FAMILY 965 



Lower leaves and often the upper with narrow, agam cleft or toothed, spreading divi- 

 sions. 

 Heads 25-50-flowered; involucre 4-5 mm. high, 5-8 mm. broad. 



Heads erect, borne singly on pedimcles 1-12 mm. long; leaves equally tomen- 



tose on both sides. 51. A. floccosa. 



Heads borne in small glomerules, sessUe, only the terminal one erect; leaves 

 less tomentose above. 52. A. candicans. 



Heads 20-30-flowered ; involucre 3 mm. high, 2.5-3.5 mm. broad. 



53. A. Flodmanii. 



X. DiSCOLORES. 



Leaves densely white-tomentose beneath, loosely floccose above, at least when young. 

 Heads very numerous in a branched leafy panicle; leaves not revolute-marglaed. 



54. A. discolor. 

 Heads fewer, usually in a narrow spike-like or racemiform inflorescence; leaves revo- 



lute-margined. 55. A. Michauxiana. 

 Leaves minutely tomentulose beneath, glabrous above. 



Heads hemispheric, nodding at least in anthesis. 56. A. graveolens. 



Heads campanulate, erect in anthesis. 57. A. tenuis. 



XI. Wrightiax.\e. 



Leaves sparingly pubescent or glabrous, green above. 



Heads erect; involucre about 2 nun. broad. 58. A. Wrightii. 



Heads nodding; involucre about 3 mm. broad. 59. A. Bakeri. 



Leaves white-tomentose on both sides. 60. A. Carruthii. 



XII. PONTICAE. 



One species. 61. A. Abrotanum. 



XIII. BiGELOVIAXAE. 



One species. 62. A. Bigelovii. 



XIV. Trtdentatae. 

 Involucre 4—5 mm. high, 3-5 mm. broad; heads 7-15-flowered (rarely 5- or 6-flowered). 

 Leaves mostly entire; heads ntmierous in a dense but not spike-like panicle. 



63. A. cana. 

 Leaves, at least some of them, 3-5-toothed at the apex; heads fewer in a narrow spike- 



Ulce panicle. 

 Plant 1-3 dm. high; branches decumbent or spreading at the base. 



64. A. arbuscula. 

 Plant about 5 dm. high, with erect strict branches. 65. A. spiciformis. 



Involucre 2-4 mm. high, 2-2.5 mm. broad; heads 1-8-flowered. 

 Leaves, at least some of them, 3-toothed at the apex. 



Shrubs 5-50 dm. high; heads numerous in ample panicles. 



Leaves cimeate. 66. A. tridentata. 



Leaves narrowly Unear-cvmeate or hnear. 67. A. angusta. 



Shrub 1-4 dm. high; heads fewer. 



Heads glomerate in dense panicles; involucre tTirbinate. 62. A. Bigelovii. 

 Heads in simple, raceme-Uke panicles; involucre campanulate. 



Heads 7-g-flowered; involucre densely canescent. 64. A. arbuscula. 

 Heads 1-6-flowered; involucre nearly glabrous. 68. A. nova. 



Leaves 3-cleft into Unear-flUform divisions. 69. A. tripartita. 



XV. Rigidae. 

 One species. 70. A. rigida. 



XVI. Ptgmaeae. 

 One species. 71. A. pygmaea. 



1. A. glauca Pallas. Perennial; stem 3-6 dm. high, silky-pubescent; leaves 

 entire, linear, 2-5 dm. long, 2-5 mm. wide, or with a few linear divisions, siUcy- 

 canescent; heads small, numerous in a large panicle; involucres about 13 mm. 

 broad ; bracts elliptic, pubescent, scarious-margined ; flowers yellow. Prairies and 

 banks: Man. — Neb. — Colo.^ — Alta.; Siberia. Plain. Jl-0. 



2. A. aromatica A. Nels. Perennial; stems mostly simple, 4-8 dm. high, 

 glabrous; leaves mostly entire, some of the lower 3-cleft, linear, 2-7 cm. long, 

 2-6 mm. wide; heads numerous, in a large leafy panicle, nodding; involucres 3-4 

 mm. broad, glabrous; bracts elliptic, dark green with scarious margins; flowers 

 browTi, the fertile ones 10-20, the sterile more numerous. Mountain valleys: 

 Alta.^ — Colo. — n Calif. — Wash.; n Mex. Submont. 



3. A. dracunculoides Pursh. Perennial; stem 5-15 dm. high, glabrous; 

 leaves narrowly linear, or some 3-cleft with similar divisions, glabrous, 3-7 dm. 

 long, 1-3 mm. wide; heads very numerous, in a compound panicle, nodding; in- 

 volucres broad, glabrous, yellowish green; bracts elliptic, obtuse; ray-flowers 

 10-20. Prairies and plains : Man. — Mo. — Tex. — Calif.— B.C. Plain — Submont. 



