COMPOSITAE. 259 



oblong-lanceolate, entire, sessile, firm, puberulent and viscidulous, 2-4 cm. long; 

 heads peduncled, erect, many-flowered; involucral bracts all acute, the outer 

 oblong-lanceolate, short, the inner linear; akenes glandular. In gravelly or 

 sandy soil, along streams. 



386. CHRYSOTHAMNUS. RABBIT BRUSH. 



Herbs or undershrubs; leaves narrow, alternate; heads mostly 

 small, with 5-30 yellow flowers, in corymbs, cymes or panicles; 

 flowers all perfect, with tubular corollas; rays none; involucre 

 imbricated; receptacle flat; pappus simple, of copious unequal 

 tawny capillary bristles; style-branches with appendages ; akenes 

 narrow, terete or angular, slightly if at all compressed. 



Chrysothamnus nauseosus (Pall.) Britt. Shrub,. 30-90 cm. high, with 

 numerous, erect, somewhat fascicled branches, these densely and permanently 

 white-woolly; leaves numerous, narrowly-linear, entire, white-woolly, some- 

 what pungently pointed, 26 cm. long; heads numerous, in terminal dense 

 corymbs; involucre about 8 mm. high; the bracts acutish, sparsely tomentose 

 or glabrate; corolla-tube villous, the lobes lanceolate; akenes linear; pappus 

 soft. Very abundant in the sagebrush region, extending up the valleys and 

 coulees and rarely on to the high prairies. 



Chrysothamnus nauseosus graveolens (Nutt.) Piper. Woolly pubescence 

 early deciduous or scanty from the first, the branches and leaves becoming 

 green and glabrous or nearly so. Very abundant with the species. 



387. CIRSIUM. THISTLE. 



Biennial or perennial herbs; leaves alternate, sessile, mostly 

 pinnatifid and prickly; heads usually large, terminal, many- 

 flowered; flowers all tubular, perfect and all alike, rarely im- 

 perfectly dioecious; involucre ovoid or spherical; bracts im- 

 bricated, in many rows, the tips scarious or prickly; receptacle 

 thickly clothed with soft bristles or hairs; pappus of numerous 

 bristles united into a ring at the base, plumose, deciduous; 

 akenes oblong, flattish, not ribbed. 



Dioecious; heads 1-1.5 cm. in diameter; perennial by 



spreading roots. C, arvense. 



Hermaphrodite; heads larger; biennials. 



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



Outer bracts spine-tipped; inner ones unarmed. 



Involucre loose, the outer bracts nearly or quite as 



long as the inner. C. edule. 



Involucre close, the outer bracts much shorter than the 



inner. 



Heads clustered, subsessile, leafy; bracts her- 

 baceous, not glandular on the back. C. foliosum. 

 Heads not clustered, peduncled; bracts coriaceous, 



glandular on the back. 



Outer bracts with spines nearly as long. C. ochrocentrum. 



Outer bracts with much shorter spines. 



Leaves canescent on both sides; flowers 



usually pink. C. undulatum. 



Leaves green above; flowers whitish. C. palousense. 



