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 unUke 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 



Not dwarfed; in- 

 florescence pan- 

 iculate: disk-cor- 

 olla under 

 long 



Herbaceous 

 species: fis.usua 

 more than is 



Dwarf; inflores- 

 cence spike-like 

 disk-corolla 



5 mm. long 



Shrubby species; 

 fis usually less 

 fhan 15 



Not sprnescent; 

 achenes and corollas 

 essentially glabrous 



Spinescent ; 

 chenes and 

 corollas long-l 



Fio. 15. — Phylogenetic chart of the speciea of Artemiaia section Dracunculus. 



