278 



GENUS ATRIPLEX. 



RELATIONSHIPS. 



Airiplex truncata is closely related to A. argentea. The fruiting bracts have undergone 

 a greater reduction in size and the free herbaceous margins have almost disappeared. 

 The latter are represented by only a narrow and minutely dentate fringe across the 

 summit. The strictly cuneate shape is quite different from anything known in argentea. 

 In some specimens of the latter the margins of the bracts are so greatly reduced as to 

 produce an appearance similar to the bracts of truncata, but the shape of the body, the 

 size, and the foliage still indicate the form as only a deviation from true argentea (e. g., 

 Hanford, California, Kearney 154 US). The connection with A. wolfi will be con- 

 sidered later (p. 279). 



Fio. 35. — Phylogenetic chart of the Atrivlex truncata group. 

 ECOLOGY AND USES. 



Atriplex truncata resembles the other vigorous annuals of the genus in ecological beha- 

 vior. It is primarily a halophyte, often growing in depressions white with alkali, where it 

 is associated with Distichlis and Chrysothamnus n. consimilis, or it may occur in less 

 alkaline soil with Sporobolus airoides. The range as to the salt-content of the soil is from 

 about 0.2 to 3 per cent. It is most vigorous in low salt-contents, becoming dwarfed in 

 soils with high amounts. In consequence it readily invades fallow fields and disturbed 

 soils of low alkalinity, where it often forms a stage of the subsere. It is exceptional 

 among related annuals in ranging to 9,000 feet in the mountains of Utah, and nearly as 

 high in those of California as the depressed form, subdecumbens. It blooms early in the 

 summer, and usually sets fruit by the middle of July. 



In spite of its ruderal habit, this species never becomes a serious weed. It is grazed 

 throughout its range, but furnishes a considerable amount of forage only in restricted 

 localities. 



