152 



GENUS ARTEMISIA. 



ness of relationship is indicated by an occasional lobe on some of the leaves, and usually 

 when this is present it has very much the shape and direction of the lobes in certain 

 subspecies of tridentata with cleft foliage. It is also significant that the inflorescence, 

 heads, and flowers of A. tridentata rothrocki so nearly duplicate those of certain forms of 

 A. cana that specimens can be identified with certainty only when lower leaves are pres- 

 ent. The geographic ranges of the two overlap along a large extent of territory, from 

 Utah and northern California nearly to the Canadian boundary, and they sometimes 

 bring the two species into the same ecologic habitat. To the south of this belt inhabited 

 by the two in common, only tridentata is found, this occurring in abundance even to 

 beyond the Mexican border, while to the north cana makes its way well up into Canada. 

 Since tridentata is of southerly origin, as has been already demonstrated, the natural 

 conclusion from a consideration of these facts of distribution is that cana is a derivative 

 of this abundant and widespread species. 



The relationships of the forms here included under A. cana have been sufficiently dis- 

 cussed in deahng with the minor variations. Table 15 supplies the evidence upon which 

 some of the conclusions were based. 



Table 15. — Variation in Artemisia cana. 



Genuine cana: 



Gallatin County, Mont 



Montana (part) 



Do 



Centennial, Wyo 



West of Laramie, Wyo 



Seven Mile Lake, Wyo 



Howell Lake, Wyo 



Fish Lake, Utah 



Little Truckee River, Calif. 



Lake County, Oreg 



Near Prineville, Oreg 



Steamboat Springs, Wyo.' . . 



Average. 



Minor variations: 



West of Laramie, Wyo.' 



Evanston, Wyo.' 



West of Rawlins, Wyo.» 

 Teton Forest, Wyo 



Average. 



166429 UC 

 29729 UC 

 29729 UC 

 70518 UC 

 CI 

 51692 UC 

 51638 UC 

 160265 UC 

 193576 UC 

 34375 UC 

 176719 UC 

 2012 Osterh 



CI 



205534 UC 



205535 UC 

 177138 UC 



4.0 

 4.5 

 5.0 



5.0 

 4.0 

 5,2 

 4.5 



.5 3.0 

 .8 3.4 

 .5 3.6 



2.3 2.5 



2.5 2.7 



2.2 2.4 



2.7 2.5 



2 5 



No. of 

 flowers 

 per head. 



Length 

 of disk- 

 corolla. 



2.9 

 2.5 

 2.5 

 2.5 

 2.7 

 2.7 



' Type of variety viscidula Osterhout. See minor variation 



' Minor variation 4 ; heads crowded and i 



ECOLOGY. 



Artemisia cana closely resembles A. tridentata in habit, as well as in the tendency to 

 form pure communities. It requires more water and hence often constitutes a subclimax 

 consocies in valleys of the northern half of the sagebrush formation. In Montana 

 especially it replaces the sagebrush, forming valley communities subclimax to the mixed 

 prairie, and making a low savannah with the grasses as it disappears before the climax. 

 In the Bad Lands of Montana and North Dakota it often plays an important role in the 

 succession, preceding the final grasses. It is regularly an indicator of greater water- 

 content, though in bad-land areas this is the result of a lack of competition. 



