306 CAKDUACEAE. 



35. COREOPSIS L. Annual or ours perennial herbs. Leaves various. 

 Heads conspicuously radiate. Involucres campanulate to hemispheric: bracts 

 distinct or nearly so, the outer narrow. Kay-flowers several: corollas with 

 yellow, discolored, or pink ligules. Disk-corollas with a funnelform throat 

 and a stout tube. Filaments mostly shorter than the anthers. Achenes with 

 entire or pinnate wings, or wingless. TICKSEED. 



1. C. tripteris L. Plants 8^30 dm. tall, glabrous or nearly so: leaf -blades 

 deeply 3-5-divided, the divisions elliptic-lanceolate or lanceolate, or those of 

 the upper leaves entire: outer involucral bracts linear, 2-3 mm. long: ligules 

 elliptic-oblong, yellow : achenes elliptic-oblong, 5-6 mm. long. Lower Sus- 

 quehanna valley. Frequent, on the river-shore and islands. Schists. Late 

 sum. 



36. BIDENS L. Annual or biennial, or rarely perennial herbs. Leaves 

 opposite, or the upper sometimes alternate: blades entire, toothed or divided. 

 Heads erect or nodding. Involucres double, the outer bracts foliaceous, the 

 inner appressed. Kay-flowers few, with white or yellow ligules, or wanting. 

 Disk-corollas with a short tube and a longer throat: lobes mostly deltoid. 

 Achenes flat, terete, or 4-angled. Pappus of 2-4 rigid, barbed awns. BUR- 

 MARIGOLD. 



Achenes spindle-shaped, gradually tapering above : ligules of the ray-flowers nearly 



white or yellowish-white. 1. B. Upinnata. 



Achenes flattened, broadest above the middle : ligules of the 



ray-flowers yellow. 

 Rays inconspicuous and caducous or wanting. 



Leaves usually undivided : pappus-awns 3 or 4. 



Disk-corollas' pale, 4-lobed : achene-margins strongly, 



retrorsely barbed throughout : involucre long. 2. B. comosa. 



Disk-corollas orange, 5-lobed : barbs of the achene- 

 margins few, directed both ways : involucre short. 3. B. connata. 

 Leaves 3-5-divided : pappus-awns 2. 4. B. frondosa. 



Rays showy or conspicuous. 



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



barbed. 



Outer involucral bracts exceeding the disk, folia- 

 ceous : ray-flowers with ligules twice the length 

 of disk or less : achenes dilated at the summit. 5. B. cernua. 

 Outer bracts rarely exceeding the disk : ray-flowers 

 with ligules 2-4 times the length of disk : 

 achenes not dilated above. 6. B. laevis. 



Leaf-blades pinnately divided : pappus-awns 2 or none. 7. B. trichosperma. 



1. B. bipinnata 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 or nearly 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. Common, in waste ground and thickets. Fall. 



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

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

 lanceolate, regularly 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 includeid: achjenes 

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

 glabrous, the 3 long awns retorsely barbed. M. Occasional, in wet places. 

 Limestones. Fall. 



