'n8 



53a. Leaves deeply pinnately parted with linear divisions; flowers 

 almost white Thistle, Cirshim pitcheri. 



53b. Leaves irregularly pinnatifid; flowers purple-pink 



Thistle, Cirsium undulatum. 

 54a. Stem-leaves entire or shallowly lobed (1 3 m. high) 



Thistle, Cirsium altissimum. 

 54b. Stem-leaves obviously pinnatifid (1 2 m. high) 55. 



55a. Leaves decurrent on the stem Thistle, Cirsium lanceolatum. 

 55b. Leaves not decurrent Thistle, f irsium discolor. 



56a. Outer and middle involucral bracts appressed, pointless or 



with weak short prickles 57. 

 56b. Outer and middle bracts erect, not appressed, acuminate 



into a long slender more or less prickly tip (4 10 dm. high) 



58. 



57a. Heads numerous 2 2.5 cm. broad, in close clusters (5 12 dm. 

 high) Canada Thistle, Cirsium arvense. 



57b. Heads few or solitary, 3 5 cm. broad (1 2 m. high) 



Thistle, Cirsium muticum. 



58a. Principal bracts with a conspicuous viscid stripe down the 

 middle; heads 6 19 cm. broad, solitary or few 



Thistle, Cirsium hillii. 

 58b. Principal bracts not viscid Thistle, Cirsium pumilum. 



59a. Receptacle not bristly; heads 3 5 cm. wide (1 3 m. high; 

 flowers pale-purple, summer) 



Cotton Thistle, Onopordum acanthium. 



59b. Receptacle bristly; heads 2 2.5 cm. wide (5 12 dm. high; flow- 

 ers purple to white, late summer) Thistle, Carduus crispus. 

 60a. Leaves basal; stem-leaves none or reduced to scales (2 8 



dm. high; flowers whitish, in spring) 61. 

 60b. Stem-leaves present; basal leaves present or absent 62. 



61a. Leaves toothed or lobed; flower-stalk not scaly 



Adenocaulon, Adenocaulon bicolor. 



61b. Leaves deeply cleft; flower-stalk scaly 197a. 



62a. Leaves compound or dissected (flowers in summer and 



autumn) 63. 

 62b. Leaves merely lobed, never truly compound or dissected 



72. 

 62c. Leaves entire or serrate 78. 



63a. Some of the involucral bracts leaf-like, longer than the heads 

 (3 20 dm. high; flowers yellow or greenish, summer and au- 

 tumn) (Beggar Ticks) 126. 



63b. Bracts short and not leaf-like 64. 



64a. Heads 7 20 mm. wide, in a flat-topped or convex cluster 

 (3 10 dm. high; flowers yellow, summer) (Tansy) 65. 



64b. Heads smaller, in spikes, racemes, or panicles (flowers yel- 

 low or greenish, late summer and autumn) (Wormwood) 66. 



