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 atthe 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. laevis. 
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. 
Involueres nearly glabrous: pappus-awns slender or wanting. 11. B.aristosa. 
Involucres hispid : achenes bidentulate. 12. B. involucrata. 
In fruit narrowly euneate-oblong, 2-2.5 mm. wide, short-awned. 13. B. trichosperma. 
Achenes 2-4 mm. long, not ciliate, bidentulate or naked. 14. B. coronata. 
1l. Bidens bipinnàta 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 
d Pins longer than the involucre, the outer slightly shorter ; awns 3-4, yellow, retrorsely 
arbed. 
In damp soil, often a weed, Rhode Island to Nebraska, Florida and Arizona. Alsoin Mexico and 
tropical America. Summer and fall. 
2. Bidens leucántha (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 comósa (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 1n- 
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 connàta 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 vulgàta 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 an 
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 frondósa 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 inyo- 
lucre 6-8, subequal, spatulate, sparsely ciliate, usually exceeding the disk: rays usu ly 
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. 
