TREES AND SHRUBS 153 



13. PICROTHAMNUS. 



Stems stout and densely branched, rigid, 1 to 4 em. high, 

 white-tomentose; leaves 4 to 8 mm. long, pedately 3 to 5-parted, the 

 divisions 3-lobed; heads globose, racemosely glomerate on short 

 leafy branehlets which become slender, persistent spines; bracts of 

 the involucre 5 to 6, broadly ovate, obtuse ; pistillate flowers 1 to 4, 

 with truncate corolla ; the hermaphrodite sterile flowers 4 to 8, the 

 corollas ventricose-campanulate from a narrow base, 5-toothed; 

 aehenes oblong-obovate. 



14. ARTEMISIA L. Sage Brush 



Annual or perennial caulescent herbs or low shrubs; foliage 

 usually pubescent; leaves alternate, blades entire, toothed, laciniate 

 or dissected ; heads small, discoid, often numerous, drooping or 

 erect; involucres various in shape, bracts in several series, the inner 

 ones successively longer; receptacle flat or hemispheric, naked or 

 sometimes pubescent, but never chaffy; flowers various, sometimes 

 all perfect and fruit producing sometimes the marginal pistillate 

 and fruit-producing, the central perfect and sometimes neutral; 

 another? entire and obtuse at the base, usually . subulate-tipped; 

 aehenes 2-ribbed, or striate, each topped by a disk. 



Heads with all the flowers fertile. 

 Leaves narrowly oblong to linear, entire. 1. A. cana. 



Leaves 3 -toothed at the apex. 



Bracts of the involucre nearly glabrous and 

 resinous, infolrescence lax, race mose; 

 plant about 1 foot high. 2. A. nova. 



Bracts of the inflorescence tometose; in- 

 florescence rather congested. 

 Shrub tall, .1 to 6 feet; inflorescence much 



branched. 3. A. tridentata. 



Shrub low a foot or so high; inflorescence 



rather simple and spike like. 4. A. arbuscula. 



Heads having two kinds of flowers; central 

 flowers sterile, the ovary abortive. 

 Shrub 4 to 6 feet high, white tometose; leaves 



filiform. 5. A. filifolia. 



