234 American Midland Naturalist Monograph No. 4 



spine-like tips; twigs slender, erect, silvery with fine gray hairs; leaves mostly 

 wedge-shaped or somewhat fan-shaped, % inch long or less, with 3 to 5 

 teeth at the tip, the teeth often 1/3 inch long; flower heads brownish-yellow, 

 mostly 5 to 9-flowered, borne in long narrow clusters, with or without short 

 branches; occurs on dry rocky hillsides and plains at higher elevations. (Syn. 

 A. arbuscula Nutt.) 



Occurrence. — YELLOWSTONE: along Yellowstone River below Yellowstone Lake. 

 GRAND TETON, in rocky locations on exjxjsed mountain sides. ROCKY MOUNTAIN. MESA 



VERDE. 



3d. Threetip Sagebrush (Var. trifida (Nutt.) McMinn). — Very 

 similar to scabland sagebrush; leaves 3 -cleft into linear divisions; flowers 

 mostly 3 to 5 in a head. (Syn. Artemisia tripartita Rydb.). 



Occurrence. — YELLOWSTONE: Upper Geyser Basin. GRAND TETON: common around 

 Jjickson Hole. ROCKY MOUNTAIN. ZION. 



4. Sand Sagebrush (Artemisia j'.lijolia Torr.). — A round-topped 

 shrub, 1 to 4 feet high, the twigs and herbage covered with fine white hairs; 

 bark of older stems smooth, dark gray or blackish; leaves very narrowly linear 

 or filiform, 1 to 3y2 inches long, the lower sometimes divided into long linear 

 divisions; flower heads yellowish, crowded in dense narrow leafy clusters 4 to 

 12 inches long. 



Occurrence. — ziON . 



5. Silver Sagebrush {Artemisia cana Pursh). — Low, silvery-gray or 

 yellowish-green shrub commonly 1 to 3 feet high (sometimes 5 feet), with 

 pungent turpentine-like odor; stems freely branching, forming rounded bushes; 

 older stems with dark brown fibrous bark; leaves silky-hairy, 2/3 to 1 (or 2) 

 inches long, narrow with pointed tips, sometimes with 1 or 2 irregular teeth; 

 flower-heads yellowish, borne in narrow leafy clusters 5 to 12 inches long, 2/3 

 to 2 inches wide; occurs usually in more or less moist and sheltered sites on 

 the plains or in mountain valleys. 



Occurrence. — glacier, rare: plains around the east entrance. YELLOWSTONE, abun- 

 dant: near east entrance; Canyon Camp; meadow near Lake ranger station; Hayden 

 Valley. ROCKY MOUNTAIN, rare: Southwest of Mount Bryant, 8,500 feet. ZiON : The 

 Narrows. 



White Burrobrush (Hymenoclea salsola Torr. 8C Gray). — Diffusely 

 branched shrub 1 to 3 feet high with a grayish-white aspect; leaves about % 

 to \y2 inches long, linear or the lower divided into slender filiform divisions; 

 male and female flowers borne in separate heads, the female heads surrounded 

 by an involucre composed of 6 roundish, silvery-papery scales often ^ 

 inch across. 



Occurrence. — ZION. GRAND canyon. 



Slender Poreleaf (Porophyllum gracile Benth.). — Widely branching, 

 ill-smelling plant about 1 to 2i/^ feet high, the stems woody only at the base; 



