402 WiEGAND : Some Species of Bidens 



* Leaves 3-foliolate, leaflets long-acuminate; heads very small (9 mm. 

 broad), on very short peduncles; achcnes very small (4.5 mm. ),tbickish^ 

 awns scarcely longer than the breadth of the achene, upwardly barbed ; 



outer involucral bracts 4. 2. B. distoiiira. 



Leaves larger, 3-5-pinnate, leallets acute to acuminate; heads larger; 

 achenes 6 mm. long; awns half as long as the achenes or more, com- 

 monly downwardly barbed ; outer involucral bracts 6-8. 



3. B. Jiielanoiarpa^ 

 Outer involucral bracts Io-i6; inner ovaic-trlangular, short; corolla stramineous; 



heads long-peduncled ; ovaries of the ray-flowers glabrous, awnless ; achenes 



broad and Hat ( j^ as broad as long) brown, nearly glabrous and smooth (rarely 



papillose) ; margins on the upper one-fourth downwardly barbed. 



4. B, froHifosa, 



£. Achenes downwardly barbed, flat or flattishj brown, glabrous or nearly so, not 



tuberculate, slightly contracted at the top, awns 2-4 ; corolla usually stramineous, 

 funnelform ; outer involucral bracts 6-8 ; leaves except in no. 6 more or le.'^s 

 petioled. 



Rays wanting (or at least not exceeding the disk) ; corolla 4 toothed. 



Achenes of small or medium size (S mm. or le.'fs) ; awns 2 (except in one 

 var. ), I the length of the achene or less; leaves incised or parted. 



[B. tripartita.'] 

 Achenes large (8-1 1 mm.; in var. 5-7 mm.); awns 3, over one half the 

 length of the achene ; leaves serrate. 5. B, comosa, 



Ray flowers present, ligulc one half longer than the disk ; corolla 5 -toothed ; awns 

 4 (rarely 2) ; leaves deeply serrate or mcised. 6. B, daitaia. 



C. Achenes usually both upwardly and downwardly barbed on the same margin, 4- 

 angled, tuberculate; awns 4 (rarely 3); corolla orange, 5-touthed, abrupdy con- 

 tracted ; leaves shnple (somethnes deeply lobed) ; outer involucral bracts 4-7 ; heads. 



commonly rayless. 



7. B. conuafa. 



Z>. Achenes downwardly barbed, biconvex or4-angIed, nearly glabrous, tuberculate on 



the angles, often striate, dark -green or blackish ; awns 2-4 ; corolla deep yellow, 

 5-toothed, at)ruptly contracted; outer involucral bracts 8; heads large, often 

 cernuous in fruit ; rays commonly long and showy ; leaves sessile. 

 Outer involucral bracts exceeding the disk, unequal, spreading, foliaceous ; rays 

 twice the length of the disk or less ; leaves long (8-16 cm.), more or less clasp- 

 ing and conhate, teeth distant ; achenes 4-angled, slightly dilated at the summit. 



8. B, cernita. 

 Outer involucral bracts rarely exceeding the disk, nearly eciual and seldom con- 



.spicuously foliaceous, slightly fleshy ; rays 2-4 times the length of the disk ; 

 achenes not dilated al)ove, flat, i -nerved on the outer face ; plant sparingly 

 branched above or simple, helianthoid in appearance ; leaves shorter, rarely 

 connate (5-I2 cm.), teeth closer. 



Leaves lanceolate, acute or short acuminate, sharply serrate, not fleshy, 

 usually ta])ering at Uie base ; branches spreading ; margin of the achene 

 straight from awns to base. o. B, lacvis. 



Leaves elliptic or oblanceolatc-oblong, acute, minutely serrate or almost entire 



L I 



somewhat fleshy, some of the upper often very broad at the base, but rarely 

 clasping ; branches strict, erect ; achenes slightly contracted at the summit. 



10. B, Nnshii, 



