GENUS 71. 



THISTLE FAMILY. 



495 



i. Bidens laevis (L.) B.S.P. Larger or Smooth Bur-Marigold. Brook Sun- 

 flower. Fig. 4505. 



Helianthus laevis L. Sp. PI. 906. 1753. 



Bidens chrysanthemoides Michx. Fl. Bor. Am. 2 : 



136. 1803. 



Bidens laevis B.S.P. Prel. Cat. N. Y. 29. 1888. 

 Bidens lugens Greene, Pittonia 4: 254. 1901. 



Annual ; glabrous throughout ; stems branch- 

 ed, erect or ascending, i-3 high. Leaves 

 sessile, lanceolate, evenly serrate or serrulate, 

 acuminate at the apex, narrowed to the some- 

 times connate-perfoliate base, 3'-8' long, i'-i' 

 wide ; heads numerous, short-peduncled, erect 

 in flower, often declined in fruit, \'-~2\' broad; 

 rays very showy, golden yellow; involucre 

 hemispheric, its outer bracts linear-oblong or 

 spatulate, equalling or exceeding the broader, 

 ovate or oblong, membranous inner ones, 

 shorter than the rays; rays 8-10, obovate- 

 oblong, obtuse; achenes cuneate, truncate, 2"- 

 4" long, retrorsely hispid on the margins; 

 pappus of 2-4 (usually 2), rigid downwardly 

 barbed awns, shorter than the achene. 



In swamps and wet meadows, Massachusetts to Illinois, Kansas, Florida, Louisiana and Mexiico. 

 Northern records of this species apply to Bidens cernua. Aug.-Nov. 



Bidens elegans Greene, of southeastern Virginia, appears to be a narrow-rayed race of this 

 species. 



2. Bidens cernua L. Smaller or Nodding Bur-Marigold. Fig. 4506. 



Bidens cernua L. Sp. PI. 832. 1753. 

 Coreopsis Bidens L. loc. cit. 908. 1753. 



Annual ; stems glabrous, or hispid, usually erect, 

 branched, 3'-3 high. Leaves sessile and commonly 

 somewhat connate-perfoliate at the base, lanceolate 

 to oblong-lanceolate, usually coarsely and sharply 

 serrate, glabrous, acuminate, 3'-6' long, i'-i' wide; 

 heads numerous, globose, short-peduncled, i'-i' 

 broad, nodding after or during flowering; rays 

 6-10, short (3"-6") or none; involucre depressed- 

 hemispheric, its outer bracts commonly ciliate, 

 often large, foliaceous and much exceeding the 

 broad, yellowish-margined membranous inner ones ; 

 achenes cuneate, 2" long, retrorsely hispid on the 

 margins; pappus of 2-4 (usually 4), downwardly 

 barbed awns, about half as long as the achene. 



In wet soil, Nova Scotia to Hudson Bay and British 

 Columbia, North Carolina, Missouri and California. 

 Also in Europe and Asia. Consists of many races, 

 differing in size. Water-agrimony. Double-tooth. Pitch- 

 forks. July-Oct. 



Bidens Eatoni Fernald, known only from brackish soil, along the Merrimac River, Mass., has 

 narrower heads and smaller achenes with awns either upwardly or downwardly barbed. 



A plant, with all the leaves pinnately divided, growing in the vicinity of Minneapolis, Minn., 

 described as Bidens connata pinnata S. Wats., may be a hybrid with B. aristosa. 



