566 



COMPOSITAE (COMPOSITE FAMILY) 



7. A. frigida. 



8. A. scopulorum. 



9. A. Pattersonii. 



subulate-acuminate appendages. Achenes obovate or oblong, mostly with 

 small epigynous disk and no pappus. 



Plants spiny; achenes with long cobwebby hairs . . . 1. A. spinescens. 



Plants not spiny; achenes not cobwebby, sometimes pubescent. 

 Flowers of two kinds, the marginal ones pistillate and fertile, the 



inner hermaphrodite but sometimes sterile. 

 Inner flowers sterile, the style mostly entire and the ovary 



aborting. 

 Plants herbaceous, or woody at the base only. 



Herbage green and glabrous, and sweet-aromatic . 2. A. aromatica. 



Herbage grayish-pubescent or canescent. 

 Heads 2-3 mm. wide; flowers yellow. 



Plants tall, 3-7 dm. high . . . . . 3. A. canadensis. 



Plants very dwarf , 5-1 5 cm. high .... 4. A. pedatifida. 



Heads 4-5 mm. wide; flowers brown . . . . 5. A. borealis. 



Plants shrubby, with filiform leaves; heads numerous, narrow, 



few-flowered . . . . . . . . 6. A. filifolia. 



Inner flowers also fertile, the style 2-cleft. 

 Receptacle beset with long woolly hairs. 



Heads small (4-5 mm. broad) and numerous 

 Heads large (6-12 mm. broad) and few or solitary. 

 Heads several in a spike-like raceme 

 Heads solitary or few in a close terminal cluster . 

 Receptacle naked (no woolly hairs among the flowers). 



A tall biennial 10. A. biennis. 



Perennials. 



Plants herbaceous or woody at the base only. 

 Silky-pubescent or glabrous, never tomentose. 



Leaves pinnate, wholly glabrous . . . . 11. A. subglabra. 

 Leaves twice 3-7-parted . . . . . 12. A. saxicola. 



Tomentose at least on the lower face of the leaves. 

 Involucres densely tomentose. 



Leaves permanently tomentose on both faces. 

 Leaves with revolute margins. 



Leaves entire, long-linear .... 13. A. natronensis. 

 Leaves pinnatifid, with narrowly linear or fili- 

 form lobes 14. A. Wrightii. 



Leaves entire, toothed or pinnatifid, oblong to 



short-linear, margins not revolute. 

 Heads small, numerous, in dense thyrse-like 



panicles . . . . . 15. A. gnaphalodes. 



Heads large (6-8 mm. in diameter), few in 



spike-like racemes . . . 18. A. paucicephala. 



Leaves usually glabrate above in age. 



Stems and involucres usually tomentose . . 16. A. ludoviciana. 

 Stems and involucres greenish and only lightly 



pubescent . . . . . 17. A. mexicana. 



Involucres glabrous or glabrate, at least in age. 



Divisions of the leaves broadly linear or lanceolate 19. A. franserioides. 

 Divisions of the leaves mostly narrowly linear. 



Leaves 1-2-pinnately parted .... 20. A. discolor. 



Leaves 3-7-parted (southern) . . . . 14. A. Wrightii. 



Shrubby, with tridentate cuneate leaves . . . 21. A. Bigelovii. 

 Flowers all alike, hermaphrodite, fertile; plants shrubby. 

 Leaves 3-toothed or 3-parted at apex. 



Leaf-segments long-linear or filiform ..... 22. A. trifida. 



Leaves toothed or lobed at apex or entire. 



Heads few, rather large, in a narrow subsimple panicle; 



leaves lobed ........ 23. A. arbuscula. 



Heads many, small; leaves 3-toothed. 

 Shrubs 4 dm. to 5 m. high; involucres tomentose . . 24. A. tridentata. 



Shrubs less than 4 dm. high; involucres glabrate . . 25. A. nova. 

 Leaves all linear and entire or nearly so .... 26. A. cana. 



1. Artemisia spinescens Eat. Bot. King's Exp. 180. pi. 19. 1871. Stems 

 stout and densely branched, rigid, 1-4 dm. high, white-tomentose : leaves 4-8 

 mm. long, pedately 3-5-parted, the divisions 3-lobed: heads globose, race- 

 mosely glomerate on short and leafy branchlets which become slender, per- 

 sistent spines; bracts of the involucre 5-6, broadly obovate, obtuse: pistillate 

 flowers 1-4, with truncate corolla; the hermaphrodite sterile flowers 4-S. the 

 corollas ventricose-campanulate from a narrow base, f>-toothed: achenes 

 oblong-obovate. (Picrothamnus desertorum Nutt. Trans. Am. Phil. Soc. 7: 

 417. 1841.) Bun-iwusii is the sheepmen's name. Alkali desert areas; Col- 

 orado to Montana and far westward. 



