A. TRIDENTATA. 



135 



Within the section proper, the common sagebrush (A. tridentata) seems to be the most 

 primitive, largely because of its connection as just mentioned with a member of the 

 obviously lower section Abrotanum. In addition to 6 subspecies and numerous minor 

 variations, it has produced 3 distinct species along the northern edge of its distribu- 

 tional area. Of these, only cana is at all common. The other two, rigida and pygmaea, 

 evidently are adaptations to peculiar and exacting conditions in the Great Basin and 

 the districts immediately northward. Both exhibit unusual modifications in the habit 



[ J6 ca/7.s 1 



Lvs. mostly entire 

 white ; heads pan- 

 iculate. Plant tall 



Lv5 pedalely cleft. 

 Silvery, heads soli- 

 tary in axils. Plant 

 dwarfed 



Lvs. pinnetifid (lower 

 onesl, green; tieads 

 spicately arranged. 

 Plant dwarfed 



Receptacle 

 Receptacle chaffy 

 naked ^ 



Flo. 19. — Phylogenetic chart of the species of Artemisia section Seriphidium. 



and cut of leaf as well as in a considerably reduced inflorescence. A. palmeri is so unlike 

 the other species that its origin is extremely doubtful. It is indicated, therefore, on 

 the chart as arising independently near the base of the group. Further data upon 

 which this outline is based will be given when discussing the relationships of each of 

 the species mentioned. 



25. ARTEMISIA TRIDENTATA Nuttall, Trans. Am. PhD. Sec. II, 7:398, 1841. Plates 18, 



19, 20. Sagebrush. 



A shrub, typically 5 to 30 or 50 dm. high but with subspecies only 1 to 5 dm. high, 

 aromatic with a pungent odor; stems erect, with usually ascending branches, the main 

 one commonly trunk-like, or the branches spreading and depressed, the old parts with 

 brown or nearly black shreddy fibrous bark, the twigs gray or white with a dense but 

 thin and fine tomentum, obscurely striate; principal leaves sessile by a narrow base 

 or apparently petioled, cuneate or flabelliform, obtuse, 1 to 4 cm. long, 2 to 5 mm. 



