260 COMPOSITAE. 



Cirsium arvense (L.) Scop. Canada Thistle. Perennial, with slender 

 creeping rootstocks; whole plant green, thinly tomentose when young, be- 

 coming glabrous, much branched, 1-2 m. high; leaves numerous, oblong- 

 lanceolate, pinnately-lobed, sessile and somewhat clasping at base, 10-20 cm. 

 long; prickles numerous, rather weak; heads small, corymbed, dioecious; 

 staminate heads globose, the flowers much exserted; pistillate heads oblong- 

 campanulate, the flowers scarcely projecting; bracts of the involucre well 

 imbricated, somewhat ciliate, the short ovate outer ones spine-tipped, the 

 inner ones lanceolate, soft-tipped; flowers pink-purple. Becoming quite 

 commonly introduced. 



Cirsium lanceolatum (L.) Scop. Bull Thistle. Stems stout, somewhat 

 woolly, usually branched, leafy to the top, 100-150 cm. high; leaves lanceolate, 

 deeply pinnatifid, hispid-pubescent but green above, white-tomentose beneath, 

 decurrent at base, 6-15 cm. long, armed with numerous stout prickles; heads 

 large, on stout leafy peduncles; involucre well imbricated, sparsely woolly; 

 bracts lanceolate, acuminate, all tipped with stout erect spiny points; flowers 

 purple. Abundantly introduced. 



Cirsium edule Nutt. Stems usually tall and nearly simple, 1-2 m. high, 

 thinly pubescent; leaves numerous, lanceolate, pinnately-lobed, pubescent 

 above, woolly beneath, but soon green and glabrate on both sides, 5-20 cm. 

 long; prickles rather weak; heads large, usually clustered, short-peduncled, 

 often surrounded by the upper leaves; involucre persistently white- woolly; 

 bracts loose, all tapering to slender rather weak prickly points, the outer 

 broader and shorter, not glandular; corolla purple, the lobes thickened at the 

 tips, shorter than the throat; pappus-bristles a little thickened at the tips. 

 Moist places in the mountains. 



Cirsium foliosum (Hook.) DC. Stems stout, erect, simple, about 1 m. 

 high, very leafy, villous and somewhat woolly; leaves lanceolate or linear- 

 lanceolate, pinnately-lobed, green and villous above, permanently white- 

 woolly beneath, 10-50 cm. long, only the lowest petioled; prickles numerous, 

 weak and slender; heads large, few, in a dense terminal cluster, surrounded 

 at base by the upper leaves which are usually reddish; involucral-bracts 

 loosely imbricated, thin, flat, the outer acuminate, sometimes with a weak 

 prickly point, the inner with scarious dilated somewhat fringed tips; flowers 

 pink, the corolla-lobes as long as or longer than the throat. North hillsides, 

 common. A peculiar plant, apparently a hybrid between this species and 

 C. palousense, sometimes occurs in its company. 



Cirsium ochrocentrum Gray. Stout and tall, 1-2 m. high; leaves mostly 

 deeply pinnatifid, white woolly on both surfaces, less so above, strongly armed 

 with stout yellow prickles; heads 2-5 cm. high, solitary on stout peduncles; 

 bracts coriaceous, the outer ones with a glandular line on the back, each armed 

 with a stout prickle as long as the bract; flowers purple or cream-colored. 

 Blue Mountains, infrequent. 



Cirsium undulatum (Nutt.) Spreng. Stout, erect, 50-200 cm. high, the 

 whole plant except the heads persistently white-tomentose, or the leaves 

 sometimes glabrate above; leaves lanceolate, pinnately-lobed or parted, 5-15 

 cm. long; prickles few or numerous, rather stout; heads large, on stout pe- 

 duncles; involucre well imbricated, the bracts thick, with a glandular spot near 

 the tip, all tipped with spreading prickly points; corollas rose-red or whitish, 

 the lobes about as long as the throat; pappus bristles a little thickened at the 

 apex. Along Snake River, common, and about Spokane. 



Cirsium palousense Piper n. comb. (Carduus palousensis Piper). Stem 

 erect, loosely branched above, 30-90 cm. high, tomentose when young, 

 becoming glabrous; leaves lanceolate, pinnatifid into rather few lobes, 

 early becoming green and glabrous _above, persistently white-woolly 



