46 



GENUS ARTEMISIA. 



Key to the Sections of Artemisia. 



Heads heterogamous, marginal flowers pistillate, disk-flowers hermaphrodite; 

 receptacle glabrous or pubescent. 

 Disk-flowers fertile, ovary normal. 



Receptacle not hairy Section I. Abrotanum (p. 46). 



Receptacle beset with numerous long hairs between disk-flowers Section II. Absinthium (p. 46). 



Disk-flowers sterile, ovary abortive; receptacle glabrous Section III. Dracunculus (p. 47). 



Heads homogamous by complete reduction of ray-flowers, disk-flowers all her- 

 maphrodite and fertile; receptacle glabrous Section IV. Seriphidium (p. 47). 



Key to the North American Species of Artemisia. 

 Section 1. Abrotanum. 



(Ray-flowers present, disk-flowers present and fertile, receptacle glabrous.) 

 Heads with more than 10 flowers; leaves never cuneate and 3-toothed at apex, although 

 sometimes spatulate and 3-cleft or 3-lobed. Herbs and shrubs. 

 Stems woody (decidedly so in the only native species, less woody in the 2 intro- 

 duced ones); leaves mostly dissected into fihform lobes; 

 achenes angled, broad and truncate at summit. 

 Principal leaves 2 or 3 times pinnatifid. Introduced species. 



Leaves 3 to 6 cm. long, lobes slender, ascending; petiole naked I. A. abrotanum (p. 49). 



Leaves 1 to 3 cm. long, lobes short, spreading; petiole aurieled at base 2. A. pontica (p. 52). 



Principal leaves mostly once pinnatifid. Native species 3. A. califomica (p. 53). 



Stems herbaceous, sometimes a little woody at base; leaves entire or variously cut 

 but seldom with truly filiform lobes; achenes smooth or ribbed 

 but scarcely angled, mostly with shght incurving at summit. 

 Plant perennial, stems from a rootstock or caudex; leaves various. 



Foliage not tomentose beneath but silvery -canescent, villous, or glabrous; 



stems 6 dm. or less high. Subalpine and Arctic plants with 



dissected leaves. 



Disk-corollas 2.5 to 3.5 mm. long (smaller in some forms of No. 4) ; heads 5 



to 9 mm. broad, except in senjavinensis and noruegica glomerata. 



Segments of leaves strongly divergent, primary divisions at right-angles to 



rachis 4. A. macrobotrys (p. 56). 



Segments of leaves pointing forward 



Leaf-lobes longer than their hairs, or leaves glabrous; lower leaves 



usually 2 or 3 times cleft or divided 5. A. norvegica (p. 57). 



Leaf-lobes exceeded and nearly concealed by their long villous pubes- 

 cence; all leaves simply cleft or entire 6. A. senjavinensis (p. 65). 



Disk-corollas 2 mm. or less long; heads 4 to 5 mm. broad. Southern Rocky 



Mountains 7. A. parryi (p. 66). 



FoUage more or less tomentose beneath, usually densely so; stems 3 to 30 dm. high. 

 Disk-corollas 3.5 to 4 mm. long; involucre 6 to 7 mm. high. A white- 



tomentose herb with very large heads and thick obtuse leaf-lobes. 8. A. stelleriana (p. 67). 

 Disk-corollas 1.5 to 3 mm. long; involucre 2.5 to 5 mm. high. 

 Leaves (except the uppermost) twice dissected and lobes obtuse; disk-flowers 

 45 to 90. 



Heads not secund; leaf-lobes linear; involucre 5 mm. high 9. A. alaskana (p. 68). 



Heads decidedly secund; leaf-lobes elUptic or oblanceolate; involucre 2.5 



to 3 mm. high 10. A. franserioides (p. 69) . 



Leaves variously cut or entire but lobes always acute; disk-flowers 3 to 40 



or rarely 50 11. A. vulgaris (p. 71). 



Plant annual or biennial, with taproot; stem erect; leaves 2 or 3 times pinnately 

 parted or divided. 

 Leaves green; divisions not filiform. 



Involucre 2 to 3 mm. high; inflorescence a dense compound spike; heads 



crowded, erect 12. A. biennis (p. 101). 



Involucre 1 to 1.5 mm. high; inflorescence a loose panicle; heads loose, often 



nodding 13. A. annua (p. 102). 



Leaves white- tomentose; divisions filiform. Mexican species with dense panicles. 14. A. klotzschiana (p. 103). 

 Heads with only 2 to 4 flowers; leaves at least in part cuneate and 3-toothed at sum- 

 mit. Low shrub -. 15. A. bigelovi (p. 104). 



Section II. Absinthium. 



(Ray-flowers present, disk-flowers present and fertile; receptacle villous.) 

 Stem 4 to 10 dm. high; divisions of leaves oblong or oblanceolate, ultimate segments 



1.5 to 4 mm. wide 16. A. absinthium (p. 106). 



Stem 1 to 4 dm. high; divisions of leaves linear, ultimate segments about 1 mm. wide. 



Plant woody and mat-like at base; stems very leafy; heads usually in panicles 17. ^4. frigida (p. 108). 



Plant not woody and mat -like at base; stems sparsely leafy; heads in racemes or 

 solitary. 

 Heads 5 to 25, 4 to 6 mm. broad; disk-flowers 15 to 30; leaves mostly twice pin- 

 natifid 18. A. seopvloTum (p. 110). 



Heads 1 to 5, 5 to 7 mm. broad; disk-flowers 30 to 120; leaves once pinnately divided 



or cleft 19. A. paUeraoni (p. 112). 



