¥@ Cirsium (Tourn.) Hill. Thistle. 
Stout perennial or biennial herbs with alternate leaves which are 
variously spinose. Heads discoid, their involucres subglobose, bell-shaped 
or urn=shaped, the bracts numerous, subulate, overlapping in many series, 
spine-tipped, the tips frequently Spreading or recurving; receptacle flat, 
bristly. Disc-corollas tubular, deeply o=cleft, often showy en masse. Achenes 
prevailingly cuneiform, more or less flattened, bearing a single series of 
deciduous softly plumose bristles. 
O Upper surfaces of leaves very harsh with short rigid 
io hairs; leaves decurrent upon the stems for 
several centimeters forming herbaceous Spinose wings }.C. lanceolatum 
—* 
o Upper surfaces of leaves soft and smooth, cobwebby or 
4 glabrous; leaves clasping the stem but not decurrent 
AInnermost series of involucral bracts 5-20 mne long; the 
; / heads 10-15 mn. broad; plants dioecious, perennial 
¥ \ with creeping rootstocks 4 [+ arvense 
7 Imnermost series of involucral bracts 20-25 mn. long; 
i (the heads 15-40 cm. broad; biennial plants without 
\ereeping rootstocks 
Involucral bracts bearing a glandular ridge near 
/the tip; heads borne at the tips of slender 
§ ( branches 5=20 cm. long, not at all crowded; 
peas leaves deeply incised, the lower surfaces 
\of all white-tomentose. 
( Flowers pink, rarely white, heads 15-20 mm. 
/o broad 3 Ce undulatumn 
6 Flowers yellowish-white, heads 25-35 mm. 
/0 broad 4 Ce palousense 
4 Involucrel bracts not bearing a glandular ridge; 
: heads crowded in the upper axils, borne on branches 
ée-5 ome long, the cluster often subtended by a 
leafy involucre; lower leaves shallowly lobed, 
[the upperfat least} nearly glabrous or cobwe bby 
beneath ; 
6 Involucral bracts glabrous 
@ Involucral bracts conspicuously dilated 
Zand flattened at the tip 4° Ce foliosun 
© Involucral bracts hardly dilated, mostly 
ZA armed with a simple spine Ce oreophilum 
6 Involucral bracts cobwebby Ce edule 
|~ [ss 
ee itis 
