180 COMPOSIT.E. (COMPOSITE FAMILY.) 



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

 foot or two hiijh : leaves from ohovate or oUong to nearli/ linear, obtuse, entire, ses- 

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

 the mosthj solitarij heads in their axils: bracts of tlie involucre connate into a 

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

 to the Dakotas and the Saskatchewan, and westward. 



26. OX Y TENIA, 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 Avhen 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. DICORIA, Torr. &Gray. 



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

 branched leaves of tlie 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 Aviih 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-rihbed : no chaff on the receptacle : leaves palmateli/ 



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 spinous tubercles around the 

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

 continent. 



* * Involucreof sterile heads not ribbed : receptacle ivith some chaff : leaves viostly 



1 to 8-pinnatiJid or dissected. 



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

 branched, a foot or two high, or taller : leaves thinnish, hipinnatifid or pinnately 

 parted with the divisions irregidarlg pinnatifd or sometimes nearly entire, on 

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

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



