COMPOSITAE. 395 



Tegules all with dilated fringed tips. C. americanum. 

 Tegules or some of them with spiny tips. 



Outer and inner tegules all with spiny tips. C. lanceolatum. 

 Outer tegules spine-tipped: inner ones unarmed. 



Heads clustered, short-peduncled; flowers pink. C. edule. 



Heads few, long-peduncled ; flowers cream-colored. C. remolifolium. 



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; tegules well imbricated, some- 

 what ciliate, the short ovate outer ones spine-tipped, the inner ones lanceolate, 

 soft-tipped; flowers pink-purple. 



A weed in cultivated ground, introduced from Europe. 



Cirsium americanum (Gray) Robinson. Stems erect, 30-90 cm. high, spar- 

 ingly branched above; leaves lanceolate, coarsely dentate to pinnatifid or even 

 pinnately parted, weakly prickly, green above, white tomentose beneath, 

 6-12 cm. long; heads mostly solitary, terminating the branches; involucre 

 2-3 cm. high; tegules with a dilated scarious tip, this lacerate and mucronate 

 on the outer ones, entire on the inner; flowers cream-colored; some of the pap- 

 pus bristles dilated at tip. 



Washington to California; rare northward. 



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; 

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

 purple. 



A very common weed, introduced from Europe. 



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 ; 

 tegules loose, each tapering to a slender rather weak spiny point, 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. 



In rich open woods and banks; the roots formerly used as food by the 

 Indians. 



Cirsium remotifolium (Hook.) DC. Woolly and cobwebby, especially 

 when young; stems erect, 1-2 m. high; leaves oblong-lanceolate in outline, 

 sinuately lobed to deeply pinnatifid, moderately prickly, white tomentose 

 beneath; heads long-peduncled; involucre 3-4 cm. high; tegules linear-at- 

 tenuate, the outer spiny-pointed, the inner scarious and lanceolate at tip; 

 flowers cream-colored; pappus bristles often thickened at tip. 



Prairies and meadows, Washington to California. 



549. ARCTIUM. Burdock. 



Coarse biennial plants with large ovate to orbicular cordate 

 leaves ; heads many-flowered ; involucre globose ; tegules numerous, 



