436 



COMPOSITAE. 



[Voi,. III. 



67. BIDENS L. Sp. PI. 831. 1753. 



Annual or perennial herbs, with opposite serrate lobed divided or dissected leaves, or the 

 uppermost alternate, and mostly large heads of both tubular and radiate flowers, or the rays 

 none, or rudimentary. Involucre campauulate or hemispheric, its bracts in 2 series, dis- 

 tinct, or slightly united at the base; the outer often foliaceous and much larger than the 

 inner. Receptacle flat or nearly so, chaffy, the chaff subtending the disk-flowers. Rays, 

 when present, neutral, mostly entire, yellow in our species. Disk-flowers perfect, fertile, 

 their corollas tubular, 5-toothed. Anthers entire, or minutely sagittate at the base. Style- 

 branches with short or subulate tips. Achenes flat, quadrangular or nearly terete, cuneate, 

 oblong, or linear. Pappus of 2-6 teeth or subulate awns, upwardly or downwardly barbed 

 or hispid. [Latin, two-toothed, referring to the achenes.] 



About 60 species of wide geographic distribution, 

 in the southern and southwestern United States. 



Besides the following, about 8 others occur 



Plants terrestrial, erect; leaves simple, or divided. 



Leaves lanceolate, serrate, undivided, rarely 3-5-lobed. 

 Rays present, large and conspicuous. 



Heads persistently erect. 1. B. 



Heads nodding after flowering. 2. B. 



Rays rudimentary, or none. 



Heads nodding after flow r ering. 2. B. cernua. 



Heads persistently erect. 



Pappus awns downwardly barbed. 



Involucral bracts not foliaceous; stem purple; flowers orange. 



Involucral bracts foliaceous; stem straw-color; flowers greenish 



4. B. 

 Pappus awns upwardly barbed. 5. B. 



Leaves some, or all of them, pinnately 1-3-parted or dissected. 

 Rays rudimentary, or none, or very short. 



Achenes flat; leaves, some or all of them, 1-3-divided. 



Leaves membranous; heads 2" -3" high. 6. B 



Leaves not membranous; heads 5" -7" high. 7. B 



Achenes linear; leaves dissected. 8. B 



Rays large and conspicuous. 



Achenes sparingly pubescent, not ciliate; pappus of 2 short teeth. 9. B 

 Achenes ciliate; pappus 2-4 subulate teeth or awns. 

 Achenes cuneate, or linear-cuneate. 

 Achenes obovate, very flat. 



Bracts of the involucre glabrous, or ciliate, short. 11. B. 



Outer bracts densely hispid, much longer than the inner. 12. B. 



Plant aquatic; submersed leaves filiformly dissected. 13. B. 



laevis. 

 cernua. 



connata. 

 yellow. 

 comosa. 

 bidentoides. 



discoidea. 

 frondosa. 

 bipinnata. 



coronata. 



10. B. trichosperma. 



aristosa. 



involucrata. 



Beckii. 



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



Sunflower. (Fig. 3938.) 



Brook 



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. 



Annual; glabrous throughout; stems 

 branched, erect or ascending, i-2 high. 

 Leaves sessile, lanceolate, evenly serrate or 

 serrulate, acuminate at the apex, narrowed 

 to the sometimes connate-perfoliate base, 

 3 / -8 / long, X /_j/ wide; heads numerous, 

 short-peduncled, erect, i / -2j / broad; rays 

 very showy, golden yellow; involucre hemi- 

 spheric, its outer bracts linear-oblong or 

 spatulate, equalling or exceeding the broader, 

 ovate or oblong, membranous inner ones; 

 rays S-10, obovate-oblong, obtuse; achenes 

 cuneate, truncate, 1" long, retrorsely hispid 

 on the margins; pappus of 2-4 (usually 2), 

 rigid downwardly barbed awns. 



In swamps and wet meadows, Quebec to On- 

 tario and Minnesota, south to Florida, Louisiana, 

 Mexico and southern California. Aug.-Nov. 



