1280 CARDUACEAE 



Rays showy or conspicuous. 



Leaf-blades undivided : pappus awns 2-4, retrorsely barbed. 



Outer involucral bracts exceeding the disk, foliaceous: ray-flowers with 



ligules twice the length of disk or less : achenes dilated at the summit. 8. B. cernua. 

 Outer bracts rarely exceeding the disk : ray-flowers with ligules 2-4 times 



the length of disk : achenes not dilated above. 



Leaf-blades lanceolate, sharply serrate, not fleshy. 9. B. lacins. 



Leaf-blades elliptical or oblanceolate, minutely serrate, slightly fleshy. 10. B. Nashii. 

 Leaf-blades pinnately divided : pappus-awns 2 or none. 

 Achenes 6-8 mm. long, ciliate : 

 In fruit broadly obovate. 



Involucres nearly glabrous : pappus-awns slender or wanting. 11. B. arifto*a. 



Involucres hispid : achenes bidentulate. 12. B. involucrata. 



In fruit narrowly cuneate^oblong, 2-2.5 mm. wide, short-awned. 13. B. trichosperma. 



Achenes 2-4 mm. long, not ciliate, bidentulate or naked. 14. B. coronata. 



1. Bidens bipinnkta L. Stem glabrous or nearly so, 4-angled, branched and rather 

 slender, 3-17 dm. high : primary leaf-segments thin, deltoid, the ultimate one lanceolate, 

 incised or lobed : outer involucral bracts 7-10, linear, shorter than the acute inner ones : 

 rays few, the ovaries awnless and glabrous, the ligules yellowish white, about equalling the 

 disk, mostly entire : disk-corolla 5-lobed : stamens included : achenes spindle-shaped, in 

 fruit much longer than the involucre, the outer slightly shorter ; awns 3-4, yellow, retrorsely 

 barbed. 



In damp soil, often a weed, Rhode Island to Nebraska, Florida and Arizona. Also in Mexico and 

 tropical America. Summer and fall. 



2. Bidens leucantha ( L. ) Willd. Stem branched, 4-10 dm. high, nearly or quite 

 glabrous : leaves firm, the segments ovate, or ovate-lanceolate, 2-8 cm. long, evenly 

 crenate-serrate : outer bracts of the involucre about 8, linear-oblong, usually shorter than 

 the inner : rays white, the ligules 1-2 cm. long, broadly cuneate, 2-3-lobed, the ovaries 

 awnless and few-barbed above : disk-corollas 5-toothed : stamens barely exserted : achenes 

 in fruit spindle-shaped, very unequal, the inner much longer than the involucre ; awns 

 2-4, short, yellow, retrorsely barbed. 



In sandy soil, common in waste places, Florida. Also in the West Indies and Mexico, and widely 

 distributed in tropical countries. 



3. Bidens comosa (A. Gray) Wiegand. Stem pale throughout, stout, 3-8 dm. high, 

 glabrous, the branches short, stout : leaves undivided, 8 cm. long, elliptic-lanceolate, regu- 

 larly serrate, acute, each attenuate into a margined petiole, or the upper sessile : heads large : 

 peduncles short and stout : outer bracts of the involucre 6-8, often 2-5 times the length of 

 the disk, erect : rays wanting : disk-corollas funnelform, pale yellow, 4-lobed : stamens in- 

 cluded : achenes large and flat, 8-10 mm. long, 3 mm. wide, brown or olive, nearly smooth 

 and glabrous, the margins to the base, the 3 long awns retrorsely barbed. 



In damp soil, Maine to Minnesota, Colorado, Georgia and Louisiana. Fall. 



4. Bidens comiata Muhl. Stem tall, sparingly branched, 3-14 dm. high, glabrous, 

 bright-green : leaf-blades undivided or some of the lower deeply parted, lanceolate to ellip- 

 tical, acuminate, tapering to the petiole, coarsely and saliently serrate : heads medium ; 

 outer bracts of the involucre 4-5, linear-spatulate, rarely exceeding the disk, glabrous : rays 

 rarely present, the ligules one-half longer than the disk, the ovaries awnless, and hairy : 

 disk-corollas campanulate above, 5-lobed, orange : achenes 4-6 mm. long, rather narrow 

 and thick, nearly black, covered with yellowish warts ; some or all marginal barbs erect ; 

 awns 4, slender, with erect or retrorse barbs. 



In swamps, New Hampshire to Minnesota, North Carolina and Missouri. Fall. 



5. Bidens vulgata Greene. Stem tall, much branched, nearly glabrous : leaf-blades 

 commonly 5-divided, the segments lanceolate, straight-veined, acute, serrate with numer- 

 ous regular sharp or bluntish teeth : heads large, 15-25 mm. wide : outer bracts of the 

 involucre 10-16, unequal, usually longer than the disk, ciliate, the inner with abruptly 

 narrowed tips : rays pale-yellow, the ligules equaling the disk, the ovaries awnless and 

 nearly glabrous : disk-corollas funnelform, pale, 4-5-lobed : stamens included : achenes 

 large, 7.5-9 mm. long, 4.5-5 mm. wide, very flat, brown or olive, nearly smooth, the 2 

 long awns and the upper part of the achene-margins retrorsely barbed. 



In damp soil, Ontario to British Columbia, North Carolina, Missouri and California. Fall. 



6. Bidens frondosa L. Stem slender, bushy-branched, nearly glabrous, 5-10 dm. 

 high or more : leaf -blades pinnately 3-divided or rarely 5-divided, the segments lanceolate, 

 serrate with sharp spreading teeth, acuminate : heads not large : outer bracts of the invo- 

 lucre 6-8, subequal, spatulate, sparsely ciliate, usually exceeding the disk : rays usually 

 present, golden yellow, the ligules equaling the disk, the ovaries hairy and with 2 short 

 retrorsely barbed awns : disk -corollas orange, 5-lobed : stamens exserted : achenes black, 

 6 mm. long, 3.25 mm. wide, cuneate, flattish, sparsely hairy and often tuberculate, the 

 barbs on the margins erect, those on the 2 awns either erect or reflexed. 



In damp soil, often a weed, New Brunswick to Nebraska, Florida and Texas. Summer and fall. 



