THISTLE FAMILY 263 



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



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



tose on both sides. 51. A. floccosa. 



Heads borne in small glomerules, sessile, 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. DISCOLORE3. 



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

 Heads very numerous in a branched leafy panicle: leaves not revolute-margined. 



54. .4. discolor. 

 Heads fewer, usuallv 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. Wrightlvnae. 

 Leaves sparingly pubescent or glabrous, green above. 



Heads erect f involucre about 2 mm. broad. 58. A. Wrightii. 



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



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



XII. PONTICAE. 



One species. 61. A. Abrotanum. 



XIII. BIGELOVIANAE. 



One species. 62. A. Bigelovii. 



XIV. Trtdentatae. 

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

 Leaves mostly entire; heads numerous in a dense but not spike-Uke panicle. 



63. A. cana. 

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

 like 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 cuneate. 66. A. tridentata. 



Leaves narrowly linear-cimeate or linear. 67. A. angusla. 



Shrub 1-4 dm. high; heads fewer. 



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

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



Heads 7-9-flowered; involucre densely canescent. 64. A. arbuscula. 

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



Leaves 3-cleft into linear-filiform divisions. 69. A. tripartita. 



XV. RiGIDAE. 



One species. 70. A. rigida. 



XVI. Pygmaeae. 

 One species. 71. A. pygmaea. 



124. PETASITES L. Sweet Coltsfoot, Butterbur. 



Leaf-blades sagittate or cordate, pinnately veined (except in P. viti folia). 

 Leaves not cleft. 



Leaves repand-denticulate, with numerous teeth. 1. P. sagittata. 



Leaves angulately and sinuately few-lobed. 2. P. frigida. 



Leaves cleft one-lliird to one-half to the midrib; lobes dentate. 



Leaves not broader than long ; only one pair of lateral veins rising from the base. 



3. P. corymbosa. 

 Leaves decidedly broader than long; two or more pairs of lateral veins rising from 

 the base. 4. P. vilifolia. 



Leaves round-reniform, pedately veined and lobed. 5. P. palmata. 



125. CROCIDIUM Hook. l. C. multicaule. 



126. PSATHYROTHES A. Gray. Velvet-rosettes. 



Leaves not beset with long hairs. 



Outer bracts obovate, larger than the inner; spreading tomentum long- villous. 



1. P. ramosissima. 

 Outer bracts oblong, not longer than the inner, erect; tomentum fine, furfuraceous. 



2. P. annua. 

 Leaves with scattered long-jointed hairs. 3. P. pilifera. 



127. HAPLOESTES A. Gray. l. H. Greggii. 



128. ARNICA L. Arnica. 



stem with several pairs of leaves, the upper not conspicuously reduced (except in A. 

 Parryi): heads usually several. 



