134 



GENUS AKTEMISIA. 



ECOLOGY AND USES. 



Artemisia spinescens is a dwarf shrubby rosette-former, suggesting A. pedatifida and 

 pygmaea in habit. It is usually found in a mixed consocies of the sagebrush climax with 

 other halophytes, and, like them, is an indicator of considerable alkali in the soil. 



Notwithstanding its spiny habit, this is a valuable browse plant on the range, especially 

 in Utah, Nevada, and eastern California, where it is known to stockmen as bud-sage. 

 This is because of its leafage, which develops ahead of that of most other shrubs in the 

 same districts. Its chief value is as an early food for sheep. Apparently authentic 

 cases of stock-poisoning have been reported for this species, but such were probably due 

 to excessive browsing without the addition of other foods. Feeding experiments con- 

 ducted by Fleming at the Nevada Station have shown that the plant is sometimes but 

 not always injurious to calves and that sheep are perhaps never killed by it, at least not 

 in the presence of other browse. The pollen has been found to be active as a cause of 

 hay-fever and is therefore used to some extent for preventing this disease in the Great 

 Basin States. 



Table 12. — Variation in Artemisia spinescens. 



No. of 



involucral 



bracts. 



No. of 

 ray-flowers. 



No. of 

 disk-flowers. 



Length of 

 disk-corolla. 



Meadow Valley, Nev 



Aztec, N. Mex 



Fort Steele, Wyo 



Carbon County, Wyo 



Meadow Valley, Nev 



Steamboat Mountain, Wyo. 



Truckee Valley, Nev 



Candelaria, Nev 



Barstow, Calif 



NY 



Gr 



NY 



Gr 



Gr 



146508 UC 



190180 UC 



193577 UC 



126503 UC 



5 6 



6 7 



5 5 

 8 



7 5 



8 7 

 4 4 



6 7 

 7 



4 4 

 4 4 

 4 4 

 4 

 4 4 



4 4 



5 4 

 5 6 



4 



13 



8 5 

 8 7 

 8 12 

 8 10 



mm. 

 2.2 

 2.3 

 2.3 

 2.4 

 2.5 

 2.2 

 2.4 

 2.4 

 3.0 



Average . 



2.4 



Section IV. SERIPHIDIUM. 

 Phylogeny of the Species. 

 All of the American members of the section Seriphidium are shrubs, this habit having 

 been developed in response to arid climates. There is at present no obvious connection 

 with any of the herbaceous species. It seems that such connection was broken very early, 

 perhaps during the Pleistocene, and that the shrubby Seriphidia developed in the south 

 at a later period. Later on, during the dry phase following the Pleistocene, they appear 

 to have moved northward, and during this process some of the present-day species were 

 doubtless evolved. This hjTJothesis very nicely accords with the fact that the most 

 highly modified forms now occupy the most northern habitats. If the American mem- 

 bers of the section arose independently of the Old World species, and there is now no 

 obvious connection between the two groups, then A. bigelotd is to be considered as most 

 closely representing the primitive stock. This has been universally classified in the 

 section Abrotanum, because of the presence of ray-flowers, but these are so few, or even 

 sometimes wanting, and the other features ally it so closely with A. tridentata that it is 

 taken to mark the borderland between the two sections. For this reason it is shown on 

 the phylogenetic chart as slightly overlapping the line between them. Its southern 

 distribution is further evidence that the later evolution of Seriphidium has been associ- 

 ated with migrations towards the north. (See the account further on of the relation- 

 ships of the subspecies, p. 141.) 



