180 COMPOSITE. (COMPOSITE FAMILY.) 



3. I. axillaris, Pursh. Stems or branches nearly simple, ascending, a 

 foot or tico Iiiyh : leaves from obovate or oblong to nearly linear, obtuse, entire, ses- 

 sile, rarely over an inch long, even the uppermost usually much surpassing 

 the mostly solitary heads in their axils ; bracts of the involucre connate into a 

 4 or 5-lobed or sometimes parted, or merely crenate cup. From New Mexico 

 to Dakota and the Saskatchewan, and westward. 



26. OXYTENIA, Nutt. 



Shrubby species, with Artemisia-like habit. 



1. O. acerosa, Nutt. Shrubby, but soft-woody, 3 to 5 feet high, canes- 

 cent, with erect branches sometimes leafless and rush-like : leaves when present 

 alternate, pinnately 3 to 5-parted into long filiform divisions, or uppermost 

 entire : heads numerous, 2 lines long, in dense panicles. Dry plains, S. W. 

 Colorado to S. E. California. 



27. DIG OKI A, Torr. & Gray. 



1. D. Brandegei, Gray. Strigulose-canescent, diffusely and alternately 

 branched leaves, of the branches oblong-lanceolate or partly spatulate, ob- 

 tuse, mostly entire, an inch or less long and with slender petiole : heads 

 sparse, racemose-paniculate ; fertile flower solitary ; its dilated-cuneate hyaline 

 subtending bract hardly surpassing the outer involucre : akene naked and 

 exserted, bordered with pectinate callous teeth connected by an indistinct sca- 

 rious margin. Proc. Am. Acad. xi. 76. Sandy bottoms of the San Juan, 

 near the boundary between Colorado and Utah. 



28. AMBROSIA, Tourn. RAGWEED. 



Coarse herbs . with mostly lobed or dissected opposite and alternate leaves, 

 and dull inconspicuous flowers : sterile heads racemose or spicate and with 

 no bracts : fertile flowers usually glomerate in axils below. 



# Involucre of sterile heads 3-ribbed : no chaff on the receptacle : leaves palmate! y 



cleft, ample, petioled. 



1. A. trifida, L. Tall and stout, 3 to 12 feet high or more, roughish 

 hispid or almost glabrous : leaves all opposite, very deeply 3-lobed or the lower 

 5-lobed ; the lobes acuminate, serrate : sterile racemes long and dense : fertile 

 heads clustered and as if involucrate by short bracts : fruit very thick, with 5 

 to 7 strong ribs or angles terminating above in spiuous tubercles around the 

 base of the conical beak. From the plains of Colorado eastward across the 

 continent. 



* # Involucre of sterile heads not ribbed : receptacle ivith some chaff : leaves most!// 



1 to 3-pinnatiJid or dissected. 



2. A. artemisiajfolia, L. Variously pubescent or hirsute, paniculately 

 branched, a foot or tico hiyh, or taller : leaves thirmish, bipinnaiifid or pinnately 

 parted with the divisions irregularly pinnatijid or sometimes nearly entire, on 

 the flowering branches often undivided : sterile heads pedicelled : fruit short- 

 beaked, armed with 4 to 6 short acute teeth or spines. A weed in waste and 



