A. PU81LLA — A. TENUI88IMA. 273 



Northern Nevada, southeastern Oregon, and northeastern California; range doubtless 

 more extensive, but the plants easily overlooked. Type locality, near Carson City and 

 on the edge of a dry alkali flat near the head of Humboldt Valley, Nevada. Collections: 

 Nevada: Humboldt Valley, 1,220 m. altitude, Watson 988 (Gr, NY, one of the type 

 collections); Camp Halleck, Humboldt River Valley, Palmer 4^4 (Gr); 4 km. west of 

 Wells, Humboldt River Valley, Hall 11033 (UC); 2 km. northeast of Wells, Hall 11034 

 (UC) ; near Carson City, Anderson 65 (Gr, NY, one of the type collections) ; same locality, 

 June 4, 1897, Jones (Herb. Jones) ; Harney Valley, Oregon, Howell 637 (Gr) ; same local- 

 ity, Cusick 1663 (DS, Gr, UC); Chat, eastern Lassen County, California, June 19, 1897, 

 Jones (Herb. Jones); "California," August and September, 1872, Torrey (US). 



SYNONYM. 

 1. Obione pnsiLLA Torrey, in Watson, Bot. King's Expl. 291, 1871. — Atriplex pusilla. 



RELATIONSHIPS. 



This was the first described species of a small group of Atriplexes characterized by the 

 small size, slender branching habit, and minute ovate fruiting bracts borne singly or at 

 least sparsely in the leaf-axils. It differs from the others, that is, from A. tenuissima and 

 A . parishi, in the even smaller and uniformly smooth bracts, as well as in details of habit 

 and leaf. These bracts are remarkably constant in their shape, which is ovate with 

 abruptly narrowed tips, and in the total absence of teeth and appendages. These char- 

 acters hold for all herbarium specimens examined and for several hundred plants studied 

 in the field, mostly in the vicinity of Wells, Nevada. 



The origin of A. pusilla is not known. In habit it is most like A. wolfi, a more easterly 

 species, but the fruiting bracts of that are so highly specialized in shape that their modi- 

 fication into the more primitive ovate type seems scarcely probable. As far as the bracts 

 are concerned, it might be looked upon as a derivative of the Calif ornian A. lularensis, 

 in which the bracts have lost their dentations and been much reduced in size. But in 

 other features these two are very unlike. When compared with the other species {tenuis- 

 sima and parishi) of its own small group, it is seen that pusilla can not be taken as the 

 beginning of this branch, because of its greatly reduced and otherwise modified bracts and 

 seeds. Neither can it be considered as a derivative of either of the other members, since 

 each of these exhibits strongly specialized features. Thus, it becomes necessary to con- 

 sider each of the three species as an isolated phylogenetic unit. Taken together they 

 form a natural group which probably originated through a divergence from the main line 

 somewhere near A. cordulata and A. tularensis and before either leaves or bracts had 

 assumed the oblanceolate, obovate, or cuneate shape. 



ECOLX)GY AND USES. 



Atriplex pusilla is a delicate annual that forms pure socies on alkaline flats between 

 bushes of Sarcobatus, or grows in disturbed spots in communities of Sarcobatu^, Distichlis, 

 and A. rosea. The plants bloom from June through August. 



This species is too delicate and too rare to be of economic importance. 



15. ATRIPLEX TENUISSIMA Nelson, Bot. Gaz. 34:359, 1902. Plate 41. 



Erect annual herb 1.5 to 3 dm. high, intricately branched throughout; branches slender, 

 elongated, ascending, sometimes zigzag, not angled, moderately white-scurfy to the base, 

 reddish except near the ends; leaves alternate except perhaps the lower, numerous, 

 sessile, lance-ovate to linear (especially in minor variation I, A. greenei Nelson), rounded 

 to the base, acute at apex, 1 to 2 cm. long, 0.2 to 0.3 cm. wide, thickish, densely gray- 

 scurfy, 1-nerved; flowers monoecious, several in each of the leaf-axils except near the base 



