KEY TO SPECIES. 47 



Key to the North American Species of Artemisia — Continued. 

 Section III. Dbaccnculus. 

 (Ray-flowers present, disk-flowers present but sterile, their achencs aborted; receptacle glabrous.) 

 Plant herbaceous, stems sometimes a little woody at base; heads more than 15- 

 flowered (including both ray- and disk-flowers). 

 Leaves mostly entire but occa.sioniilly with an irregular lobe or lower leaves some- 

 times :i- to 5-cleft 20. A. dracunculus (p. 1 15). 



Leaves pinnatifid, bipinnatifid, or dis.sected, except the uppermost. 



Disk-corollas campanulate, 1.5 to 3 mm. long; lower leaves 2 to 10 cm. long 



mcluding petiole; inflorescence 1 to 10 cm. broad 21. A. campestris (p. 120). 



Disk-corollas tubular-funnelform, 3 to 3.5 mm. long; lower leaves rarely over 2 



cm. long including petiole; inflorescence about 0.5 cm. broad. . 23. A. pedatifida (p. 131). 

 Plant shrubby but sometimes dwarfed; heads less than 15-flowered. 

 Achenes and corollas glabrous or only minutely pubescent; plant not spinescent. 

 Inflorescence loosely paniculate; involucre about 1.5 to 2 mm. high; disk-corollas 



2 mm. or less long; .shrub normally 3 to 10 dm. high 22. A. filifolia (p. 130). 



Inflorescence spike-like; involucre about 3 mm. high; disk-corollas 3 to 3.5 mm. 



long; shrub dwarf (1.5 dm. or le.ss high) 23. A. pedatifida (p. 131). 



Achenes and corollas cobwebby with long hairs; plant spinescent 24. A. spineacena (p. 132). 



Section IV. Seripiiidium. 

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

 Receptacle not chaffy; leaves tomentose on both sides, except in pygmaea and one 

 subspecies of tridentata. 

 Leaves gray, wholly covered with a canescent or silvery tomentum, either entire 

 or palmately toothed, cleft, or parted. 

 Heads in spikes or panicles, at least the upper ones longer than their subtending 

 bracts. 

 Leaves (except the uppermost entire ones) cuneate to spatulate-linear in outline, 



mo.stly toothed or parted 25. A. tridentata (p. 135). 



Leaves linear, somewhat tapering to each end, all entire or rarely with a few 



teeth or lobes, silvery-canescent 26. A. cana (p. 150). 



Heads sessile in axils, all much exceeded by their subtending leaves; divisions of 



leaves linear, mostly 5 to 15 mm. long, silvery 27. A. riffida (p. 153). 



Leaves green, glandular-puberulent, lower pinnatifid with 5 to 7 lobes 28. A. pygmaea (p. 154). 



Receptacle chaffy with scarious bracts which subtend most of the flowers; leaves 



green above, tomentose beneath 29. A. palmeri (p. 155). 



Artificial Key to the North American Species of Artemisia. 



Plant an herb, stems often thickened and perennial at base but never decidedly woody. 

 Duration annual or biennial; plant with a taproot. 



Inflorescence' spike-like but in reality composed of a series of short spikes 12. A. biennis (p. 101). 



Inflorescence a panicle. 



Leaves gray, densely hairy, lobes thread-like. Mexico li.'A. klotzsehiana (p. 103). 



Leiives green, glabrous or spar.sely hairy when mature, plane. 



Achenes all well formed and fertile 13. A. annua (p. 102). 



Achencs of central flowers aborted and sterile (subspecies caudata of) 21. A. campestris (p. 120). 



Duration perennial; plant with branching crown or with rootstocks. 

 Segments of leaves mostly 2 mm. or more wide, linear to lanceolate or ovate, or 

 leaves entire and over 2 mm. wide. 

 Lobes of leaves obtuse. 



Involucre 6 to 7 mm. high; corolla of disk-flowers 3.5 to 4 mm. long 8. A. slelieriana (p. 67). 



Involucre 2.5 to 5 mm. high; corolla of disk-flowers 1.5 to 2.5 mm. long. 

 Receptacle without hairs between flowers. Native. 



Heads growing from both sides of branch (not secund). Alaskan species. 9. A. alaskana (p. 68). 

 Heads growing from only one side of branch (secund). Southwestern 



United States 10. A. franserioides (p. 69) . 



Receptacle densely long-hairy between flowers. Introduced 16. .4. absinthium (p. 106). 



Lobes of leaves acute, or leaf itself acute if not lobed. 



Leaves with a dense tomentose or woolly pubescence, at least beneath 11. A. mdgaris (p. 71). 



Leaves with silky or spreading pubescence or glabrous. 



Central flowers with normal achenes; leaves mostly pinnatifid or cleft 5. A. norvegica (p. 57). 



Central flowers without achenes; leaves mostly entire or with few lobes. . . 20. A. dracunculus (p. 115). 

 Segments of leaves mostly 1 mm. or less wide, linear or filiform, rarely elliptic 

 or ovate in dwarf plants, or leaves entire and less than 2 mm. 

 wide. 

 Receptacle not evidently hairy between flowers. 

 Leaves mostly entire, a few cleft into 2 or 3 short ascending lobes, green .... 20. A. dracunculus (p. 115) 

 Leaves pinnatifid into 5 to 10 or more spreading divisions. 



Achenes present only in marginal flowers, those of central flowers wanting. 21. A. campestris (p. 120). 

 Achenes present in all flowers. 



Foliage tomentose or woolly, especially beneath; leaf-lobes linear- 

 filiform (mostlj' subspecies wrighti of) 11. A. vulgaris (p. 71). 



' Throughout this key the term inflorescence is used to indicate the assemblage of heads. Strictly speaking, each head 

 is an infloreacence in itself. 



