114 



GENUS ARTEMISIA. 



of pattersoni. This character, however, is exceedingly variable in other species of Arte- 

 misia. The most important differences not brought out in the table are the large heads 

 and simply cut foliage of pattersoni as contrasted with the smaller heads and mostly 

 dissected foliage of scopulorum. 



ECOLOGY AND USES. 

 Artemisia pattersoni closely resembles A. scopulorum in life-form and ecological rela- 

 tions. However, it never forms societies, but is restricted to small clans, often more or 

 less mixed with A. scopulorum. No uses are known for this species. 



Section III. DRACUNCULUS. 

 Phylogeny of the Species. 



One species of the section is so unlike the others that it is considered as representing a 

 very early divergence. This is A. spinescens. Since it was once taken as the type of the 

 proposed genus Picrothamnus, its relationships have been already discussed in detail (see 

 p. 32). The remaining four species are readily divisible into two wholly natural pairs. 

 A. dracunculus and A. campestris are presumably of Old World origin, although both are 

 now abundantly represented in America by a number of subspecies. Their migration 

 seems to have been by a route across or around the North Atlantic, since they are not 



Lvs.entire , or a Lvs. p'mnatifid 

 few simply cleft (except upper) 



Not dwarfed; In- 

 florescence pan- 

 iculate: disK-cor- 

 olla unaer 2 mm. 

 long 



Herbaceous 

 species : f Is. usually 

 more than ts 



Dwarf; inflores- 

 cence spike- like; 

 disk-corolla 

 3 to 3.5 mm. long 



Shrubby species ; 

 fls. usually less 

 than 15 



Not spinescenf ; 

 achenes and corollas 

 essentially glabrous 



Spinescent ; 

 chenes and 

 corollas long-hairy 



Fia. 15. — Phylogenetic chart of the species of Artemiaia section Dracuncutua. 



