138 GENUS AHTEMISIA. 



which are themselves 3-cleft, or the uppermost ones linear and entire; inflorescence 

 loosely paniculate, 1 to 3 cm. broad; heads ovoid, 2.5 mm. or less broad; involucre 

 canescent; flowers 5 to 8; corolla 2 to 2.5 mm. long; achenes resinous-granuliferous. 

 {A. trifida Nuttall, Trans. Am. Phil. Soc. II, 7:398, 1841.) Northern Rocky Mountain 

 and Great Basin States, on open plains ; Montana to Colorado and west to eastern Oregon 

 and Washington, apparently also in eastern California and reported from British Colum- 

 bia. Type locality, plains of the Rocky Mountains. Collections: Type collection, 

 Nuttall (Phila, with a piece of A. rigida); Alaska Basin, Montana, Nelson 6809 (Gr, 

 NY, US); Big Butte Station, Idaho, Palmer 497 (US); Teton Forest, northwestern 

 Wyoming, Tweedy 668 (NY); Laramie Plateau, Wyoming, September 9, 1919, ^aZi 

 (UC); near Lancaster, Mojave Desert, California, Parish 1177 (identical with Nuttall's 

 plants, according to Gray); eastern Oregon, Cusick 2501 (Gr, NY, UC, US); base of 

 Cascade Mountains, Washington, 1882, Brandegee (UC). 



25e. Artemisia tridentata arbuscula (Nuttall). — Shrub 1 to 4 dm. high, stiffly 

 and irregularly much branched, the lower branches spreading and often spinescent, the 

 twigs slender and erect; pubescence gray, appressed; leaves cuneate or flabelliform, 

 mostly 1.5 cm. or less long, 3- to 5-lobed or cleft at apex, the lobes sometimes 10 mm. 

 long, the uppermost entire; inflorescence spike-like, 1.5 cm. or less broad; heads campanu- 

 late, 2.5 to 3 mm. broad; involucre canescent; flowers 5 to 9; corolla 2 to nearly 3 mm. 

 long; achenes granuliferous. {A. arbuscula Nuttall, Trans. Am. Phil. Soc. II, 7:398, 

 1841, in part, the remainder being subspecies nova.) Northern Rocky Mountains and 

 Great Basin, on dry, rocky hillsides and plains, especially on the scab-lands; Idaho, 

 Wyoming, and western Colorado to eastern California and Washington. Type locality, 

 arid plains of the Snake River. Collections: Type collection, Nuttall (Gr, Phila.; the 

 specimen at Philadelphia is a young plant with racemose inflorescence, the involucres very 

 tomentose, and the whole appearance that of arbuscula as here described rather than of 

 nova) ; near Evanston, Wyoming, September 12, 1919, Hall; Hay den Flats, Routt County, 

 Colorado, Osterhout 2260 (NY) ; Mount Rose, western Nevada, Heller 9883 (DS, Gr) ; 

 near Olancha Peak, southern Sierra Nevada, California, Purpus 1868 (UC); Mono 

 County, California, August, 1898, Congdon (UC); ridge northwest of Donner Pass, 

 Cahfornia, Heller 12914 (Gr, SF, UC, US, see minor variation 9); divide between 

 American and Rubicon Rivers, Eldorado County, California, Kennedy 203 (UC); near 

 Hay Creek, eastern Oregon, Leiberg 859 (DS, Gr, UC, US) ; Yakima region, Washington, 

 Brandegee 146 (UC). 



25/. Artemisia tridentata rothrocki (Gray). — Shrub 1 to 8 dm. high, or perhaps 

 more, branching from the base to form low rounded bushes with erect twigs, not espe- 

 cially rigid ; pubescence gray, appressed, sometimes viscidulous ; leaves elongate-cuneate, 

 1 to 4 cm. long, 3-toothed at apex, or 3-cleft and the lobes toothed, many of the upper 

 or even some below the inflorescence linear and entire; inflorescence spike-like or very 

 narrowly paniculate, 1 to 3 cm. broad; heads campanulate, 3 to 4.5 or rarely 5 mm. 

 broad ; involucre varying from greenish-yellow or straw-color and only obscurely tomentu- 

 lose as in the original rothrocki, to closely canescent (minor variation 7, A. spidformis 

 Osterhout), somewhat viscidulous in the green form (outer bracts broadly ovate and 

 canescent, inner ones broadly elliptic and scarious in minor variation 18, A. vaseyana 

 Rydberg) ; flowers 6 to 15, rarely to 20; corolla 2.5 to 3.5 mm. long; achenes only granular. 

 {A. rothrocki Gray, Bot. Cahf. 1:618, 1876.) Widely distributed in the western United 

 States but wanting over much of the area, confined to the higher zones in the mountains : 

 Rocky Mountains of Wyoming, Colorado, and Utah; San Bernardino Mountains of 

 southern California; Olancha Peak, in the southern Sierra Nevada of California, to 

 eastern Washington, western Nevada, and Idaho. Type locality. Sierra Nevada of 



