COMPOSITAE (COMPOSITE FAMILY) 575 



exceeding the internodes; the upper and smaller pairs sessile and distant, giv- 

 ing the upper half of the stem a naked-scapose appearance: inflorescence of 

 about 5 heads in a close corymb; terminal head much the largest, 10-12 mm. 

 high and about as broad ; involucral bracts in 2 series, narrowly oblong, ob- 

 tusish, the tip tinged with purple and tomentose-ciliate : rays few, short, broad: 

 tube of disk-corollas pubescent, the glabrous throat scarcely dilated: achenes 

 very minutely pubescent: pappus dirty- white, minutely scabrous. Southern 

 Wyoming (Saratoga) and Colorado (Sapinero). 



16. Arnica Parryi A. Gray, Am. Nat. 8: 213. 1874. Stems 2-5 dm. high, 

 slender, simple, somewhat hirsutely pubescent and above glandular: leaves 

 commonly denticulate; radical oval to ovate-oblong, 3-8 cm. long, abruptly 

 or cuneately contracted at base into a short-margined petiole; the cauline re- 

 mote, narrower: involucre hirsute and glandular, 10-14 mm. high; heads ray- 

 less, occasionally some outermost corollas ampliate: achenes glabrous or with 

 a few sparse hairs. [A. eradiata (Gray) Heller.] Throughout our mountains 

 and westward. 



89. TETRADYMIA DC. 



Low rigid shrubs of arid districts. Herbage clothed with dense and matted 

 or floccose wool which is deciduous in some species. Leaves alternate, entire, 

 solitary or fascicled, the primary ones often modified into spines. Involucre 

 cylindric to oblong, composed of 4-6 firm, concave, overlapping bracts which 

 are often enlarged and thickened at base. Heads discoid, 4-9-flo wered . Re- 

 ceptacle flat, small. Corollas yellow; lobes spreading, longer than the short- 

 campanulate throat, much shorter than the elongated tube. Anthers exserted, 

 sagittate at base, the tips triangular-lanceolate. Style-branches flat, obtuse. 

 Achenes terete, faintly 5-nerved. Pappus of fine and soft scabrous capillary 

 bristles, white or whitish. 



Involucres 4-flowered; pappus very copious; achenes either villous or gla- 



brate. 

 Wholly unarmed shrubs. 



Leaves permanently woolly-canescent . . . . . . 1. T. inermis. 



Leaves small, fascicled, green 2. T. glabrata. 



Spinescent from the axils . . . . . . . . . 3. T. Nuttallii. 



Involucres 5-9-flowered; pappus less copious; achenes white-tomentose . 4. T. spinosa. 



1. Tetradymia inermis Nutt. Trans. Am. Phil. Soc. 7: 415. 1841. Wholly 

 unarmed, the shrubby base tufted, much-branched, spreading-assurgent ; the 

 herbaceous annual stems numerous, somewhat fascicled, simple or branched, 

 erect, 8-15 cm. long, permanently canescent with a dense, appressed tomen- 

 tum: leaves numerous but not fascicled, narrowly oblong with tapering ends, 

 acute at apex, nearly sessile, like the stems permanently canescent, 15-25 mm. 

 long, midrib usually evident, the pair of lateral nerves obscure: flowers in very 

 compact terminal clusters of 10-20 heads with bract-like leaves intermingled: 

 heads 12-14 mm. high, 4-bracted and 4-flowered: pappus copious; achenes 

 villous. (T. multlcaulis A. Nels. Bull. Torr. Bot. Club 26: 482. 1899; T. 

 linearis Rydb. Bull. Torr. Bot. Club 32: 130. 1905.) Throughout our range 

 and scarcely distinguishable from T. canescens DC., which is confined mostly 

 to the Pacific States. 



2. Tetradymia glabrata Gray, Pacif. R. R. Rep. 11: 122. pi. 5. 1855. Shrub 

 3-10 dm. high with slender spreading branches, whitened with loose at length 

 deciduous tomentum: leaves at length naked and green, primary ones slender- 

 subulate, cuspidate, on young shoots appressed, 12 mm. long; those of the 

 fascicles in their axils spatulate-linear, fleshy, pointless: heads mostly short- 

 pedunculate; involucre often glabrate: achenes villous. Scarcely in our range, 

 but reaching Utah from the west. 



3. Tetradymia Nuttallii T.&G.F1. 2: 447. 1841. Shrubby, much-branched, 

 woolly when young, canescent: primary leaves mostly converted into subulate 

 spines; the others densely fascicled in their axils, thickish, linear-spatulate, 

 obtuse, the tomentum somewhat deciduous: heads fascicled and in corymbose 



