1000 FLORA. 



broad; outer bracts of the invoiucre linear, obtusish, much narrower than the ovate- 

 oval or ovate-lanceolate, acute inner ones; rays 6-io, yellow, obtuse, achenes oblong 

 to obovate, narrowly winged, emarginate; pappus none. In moist woods and 

 thickets, Penn. to Wis., Kans., Va., Fla. and La. July-Oct. 



67. BIDENS L. (See Appendix.) 



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 campanulate or 

 hemispheric, its bracts in 2 series, distinct 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, ob- 

 long, or linear. Pappus of 26 teeth or subulate awns, upwardly or downwardly 

 barbed or hispid. [Latin, two-toothed, referring to the achenes.] About 75 spe- 

 cies of wide geographic distribution. Besides the following, several others occur 

 in the southern and western U. S. 

 Plants terrestrial, erect ; leaves simple, or divided. 



Leaves lanceolate, serrate, undivided, rarely lobed (pinnately divided in B. connata 

 pinnata. 



Rays present, large and conspicuous, twice as long; as the disk or longer. 

 Heads usually erect ; rays oval ; leaves lanceolate, many-toothed. 



1. B. laevis. 

 Heads nodding ; rays linear-oblong; leaves narrowly lanceolate, fine toothed. 



2. B. elegans. 

 Rays small, not more than twice as long as the disk, sometimes very short of 



wanting. 



Heads nodding after flowering. 3. B. cernua. 



Heads persistently erect. 



Pappus-awns downwardly barbed. 



Involucral bracts not foliaceous; stem purple; 



flowers orange. 4. B. connata. 



Involucral bracts foliaceous ; stem straw-color ; flowers greenish 

 yellow. 



Outer involucral bracts erect or nearly so ; lower leaves petioled. 



5. B. comosa, 

 Outer involucral bracts spreading; leaves sessile. 



6. B. acuta. 

 Pappus-awns upwardly barbed. 7. B. bidentoides. 



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

 Rays rudimentary, none, or very short. 



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

 Outer involucral bracts, 4-8 ; aclienes nearly black. 



Achenes 4-4.5 mm. long ; awns very short ; outer bracts 4. 



8. B. discoidea. 

 Achenes 6 mm. long ; awns half as long as the achene ; outer 



bracts 6-8. 9. B. frondosa. 



Outer involucral bracts 10-16 ; achenes brown. 10. B. vulgata. 

 Achenes linear ; leaves dissected. n. B. bipinnata. 



Rays large and conspicuous. 



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



12. B. corona fa. 

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



Achenes cuneate, or linear-cuneate. 13. B. trichosperma. 



Achenes obovate, very flat. 



Bracts of the involucre glabrous or ciliate, short. 



14. B. aristosa. 

 Outer bracts densely hispid, much longer than the inner. 



15. B. involucrata. 

 Plant aquatic ; submersed leaves filiformly dissected. 16. B. Beckii. 



I. Bidens laevis (L.) B.S.P. LARGER OR SMOOTH BUR-MARIGOLD. BROOK 

 SUNFLOWER. (I. F. f. 3938.) Annual; glabrous throughout; stems branched, 

 erect or ascending, 3-6 dm. high. Leaves sessile, acuminate at the apex, narrowed 

 to the sometimes connate-perfoliate base, 7-20 cm. long, 6-25 mm. wide; heads 



