340 GENUS ATRIPLEX. 



RELATIONSHIPS. 

 Atriplex confertifolia is the central and by far the most abundant and widespread 

 member of a close group of three species, the other two being spinifera and parryi. All 

 of these have developed a decidedly spinose habit, which, however, is found also in 

 certain forms of A. lentiformis, a species otherwise very different. In addition to the 

 spinose habit, the confertifolia group is marked by characters of the fruiting bracts not 

 found elsewhere in the genus. The bracts of each pair are firmly united at the base 

 into a small indurated thickened body from the upper portion of which the free margins 

 are developed into a pair of thin, flat wings standing face to face and much broader 

 than the body itself. Differences in the shape of the body and in the size and shape 

 of the wings constitute the principal characters used to differentiate the species of the 

 group. 



ECOLOGY. 



Atriplex confertifolia ranks next to Artemisia tridentata in importance as a consocia- 

 tion of the Basin sagebrush association. In Nevada it is often more abundant than 

 sagebrush, owing to the prevalence of hard, stony, alkaline soils on benches and slopes. 

 Over much of its range it regularly mixes or alternates with Artemisia and its associates, 

 such as Grayia, Chrysothamnus, and Tetradymia. It endures alkaline soils better than 

 most of these and its most typical position, both as to topography and succession, is 

 in a zone between such strongly halophytic dominants as Sarcobatus or Atriplex nut- 

 talli and corrugata on the one hand and sagebrush on the other. It may even occur 

 on alkali flats with such marked halophytes as Salicornia, and is frequently associated 

 with Kochia vestita, and in Nevada with Artemisia spinescens. It is a characteristic domi- 

 nant of the bad lands of the Great Basin, especially the Cretaceous ones of the Mancos, 

 Fort Steele, and Lewis formations, covering the less alkaline slopes between Atriplex 

 nuttalli at the base and the sagebrush climax above. 



Kearney, Briggs, Shantz, McLane, and Piemeisel have found the salt-content to 

 range from 0.06 per cent in the first foot to 0.09 per cent in the fourth foot where the 

 plants were exceptionally large and healthy, while the average range was from 0.07 in 

 the first foot to 0.93 per cent in the fourth foot (Indicator significance of vegetation in 

 Tooele Valley, Utah. Jour. Agr. Res. 1:396, 1914). 



USES. 



Chiefly because of its great abundance over large areas where other browse and 

 forage plants are scarce, the shadscale is of much value to the stock interests in western 

 North America. It is used especially as a winter browse for sheep in Nevada and 

 adjacent States and to some extent also for cattle, the spines, however, interfering with 

 its use by the latter. Otherwise the species is of economic interest only as a cause of 

 hay-fever. It is almost certain that the pollen extracts could be advantageously used 

 for purposes of desensitization against this malady in the case of some patients, as 

 explained under A. rosea (p. 260). 



45. ATRIPLEX SPINIFERA Macbride, Contr. Gray Herb. n. s. 53:11, 1918. Plate 57. 



Spinescale. 



Erect shrub, very woody throughout, rigidly branched and spiny, normally much 

 taller than broad, 3 to 15 dm. high; branches not angled, but sometimes striate, stout, 

 mostly erect, white-scurfy at first, glabrate but still very pale, the old bark gray, splitting 

 longitudinally on the surface and exfoliating; leaves either crowded or rather sparse, 

 deciduous from the twigs which then become modified into rigid horizontal or widely 

 divergent spines, alternate, mostly short-petioled, the upper sessile, deltoid-ovate or 

 elliptic, cuneate at the base or the sessile ones truncate, obtuse at apex, 1 to 2 cm. 

 long, 0.5 to 1.5 cm. wide (undeveloped leaves of the ultimate twigs often much smaller, 

 as in the type specimen), entire or especially those on sterile shoots subhastate, thinnish, 



