A. POWELLI. 



291 



Herbarium, Salt Lake City, include Marysvale, Sunnyside, and Cainville, all in Utah. 

 Additional Wyoming localities represented at the Rocky Mountain Herbarium are 

 Point of Rocks, Middle Fork of Powder River, and Claremont, Johnson County. 



MINOR VARIATIONS. 



1. Atriplex nelsoni Jones, Contr. West. Bot. 11:21, 1903.— Described from plants in which the fruiting 

 bracts are mostly smooth on the sides, the margins bearing a few large herbaceous lobes. The shape of the 

 terminal lobe, the venation of the leaf, and other characters positively assign this to powelli, which species 

 apparently was overlooked or misunderstood when the description of nelsoni was prepared. 



2. A. PHiLONiTRA Nelson, Bot.Gaz. 34:358, 1902.— The description and the types are both as in genuine 

 powelli. Type locality, Laramie River, Wyoming. 



RELATIONSHIPS. 



The characters of this species are so remarkably fixed that it can not be connected 

 closely with any other. It appears to be not a modification of any existing form but the 

 end of a branch from near the beginning of the argentea group. It is not primitive, as is 

 indicated by the absence of a perianth in the pistillate flowers, the unusual development of 

 the fruiting bracts, and the attainment of partial dioecism. In this last-named feature 

 it has progressed far beyond its nearest allies. In the Green River district of eastern 

 Utah the differentiation into pistillate and staminate individuals is so marked that the 

 prevailing sex may be determined at a glance.' Here the pistillate plants are strictly 

 erect, with more numerous and larger leaves than occur on the staminate. They bear 

 no male flowers. On the other hand, the staminate plants bear a few pistillate bracts 

 in the lower axils of the inflorescence. The staminate flowers open before the pistillate 

 on neighboring plants. At Green River Station some plants have about as many 

 staminate as pistillate flowers, a proportion also found on herbarium sheets from other 

 localities. Along the Laramie River, Wyoming, the axial branch of each plant is usually 

 wholly staminate, according to Nelson (Bot. Gaz. 34:358, 1902, under A. ■philonitra) . 

 The type material at the Gray Herbarium consists of 3 plants, 2 purely pistillate, the 

 third about half pistillate and half staminate. None of these are very leafy. Thus it 

 seems that this species is in a progressive stage of evolution and that it is headed toward 

 a complete dioecism like that obtaining in the shrubby species of Atriplex. The shape 

 and venation of the leaves supply evidence that it is perhaps as close to A. argentea as 

 to any other species. 



Some taxonomic confusion has come about through a misunderstanding of A. powelli. 

 Perhaps this resulted from the inadequate descriptions of the peculiar fruiting bracts. 

 For some time collections were labeled as a form of A. expansa, with which it can not 

 possibly be confused when attention is given to the bract characters or even to the vena- 

 tion of the leaf. This led Nelson to redescribe it as A. philonitra, and Jones, who had a 

 slightly different form, as A. nelsoni. These names were reduced into synonymy by 

 Standley (N. Am. Fl. 21:48, 1916), who, having access to the type specimens of powelli, 

 noted the practical identity of all three. 



ECOLOGY AND USES. 



Atriplex powelli is a characteristic indicator of abundant surface alkali, usually occur- 

 ring in pure stands in alkaUne valleys and plains. It regularly forms the initial consocies 

 in such areas throughout most of southern Wyoming, Colorado, Utah, and northern New 

 Mexico and Arizona. The perennial zone around is occupied by A. nuttalli and corrugata, 

 by the first alone, or with Sarcobatus or Sporobolus airoides. While it may grow in 

 depressions along roadsides, it rarely becomes a true ruderal, probably owing to the com- 

 petition of more successful halophytes, such as Salsola. The plants flower from July 

 through October. 



Watson states that the fruits are collected by the Indians for food (Proc. Am. Acad. 

 9:115,1874). 



