346 LXXV. COMPOSITE. Bidens. 



10. C. ROSEA. Nutt. (Calliopsis. Spreng.) Rose-red Tickseed. 



St. branched; Ivs. opposite, 1-veined, linear, entire; ped. short; outer 

 ^•■ales very short ; rays obscurely tridentate. — % A very delicate species, in wet 

 grounds, Mass. Dr. Robbliis! to N.J. Stem slender, erect, 8 — 16' high. Leaves 

 1—2' long, scarcely 1" wide, clothing the stem. Heads few, small. Rays rose- 

 color, varying to white. Disk light yellow. Jl. Aug. 



46. BID ENS, 



Lat. bidens, two-toothed ; the achenia have 2 (or more) barbed teeth. 



Involucre nearly equal, double, scaly or leafy at the base ; rays 

 few, neutral ; disk perfect ; receptacle chaffy, flat ; pappus of 2 — 4 

 awns, rough backwards ; achenia quadrangular. — Lvs. opposite. Rays 

 often wanii?ig. 



* Rays inconspicuous or 0. 



1. B. PRONDOSA. Leafy Burr-Marigold. 



Ms. discoid ; outer invol. 6 times as long as the flower, its leaflets ciliate 

 at base; lotuer lvs. pihnate, upper ones ternate, lanceolate, serrate. — A com- 

 mon weed, in moist, cultivated fields throughout Can. and U. S., olten called 

 beggar ticks, from the 2-horned achenia which adhere to every one who passes 

 by it. Stem 2f high, sending out many spreading branches. Lower leaves in 

 3s or 5s. Flowers in clusters at the end of the branches, without rays, yellow, 

 surrounded by a large and leafy involucre. Aug. Sept. 



2. B. coNNATA. Willd. (B. tripartita. Bv}.) T'rifid Burr- Marigold. 



Smooth; Its. lanceolate, serrate, slightly connate at base, lower ones most- 

 ly trifid ; outer scales longer than the head, leafy; ach. with 3 awns. — (J) In 

 swamps and ditches, Can., N. Eng. to Mo. Stem 1 — 3f high, smooth and 4-fur- 

 rowed, with opposite branches. Leaves opposite, smooth, serrate, the lower 

 ones often divided into 3 segments, the rest generally entire, lanceolate, sharply 

 serrate and somewhat connate. Flowers .terminal, solitary, without rays, con- 

 sisting only of the tubular, yellow florets, surrBunded by a leafy involucre. Aug. 



3. B. CERNUA. Wa.ler Burr-Marigold. 



Fls. subradiate, cernuous ; outer invol. as long as the flower; lvs. lanceo- 

 late, subconnate, dentate. — In swamps and ditches, Can. to Penn. Stem 1 — 2f 

 high, purplish, branched, round at base, striate above, branches opposite, leaves 

 opposite, somewhat connated at base. Flowers yellowish-green, finally droop- 

 ing, generally with yellow rays about 8 in number. Aug. — Oct. 



4. B. Bi FINN ATA. Spanish Needles. 



Smooth ; lvs. bipinnate ; Ifts. lanceolate, pinnatifid ; hds. subradiate ; outer 

 invol. the length of the inner. — -"(X) Grows in waste places, N. Y. Sartwell, Conn. 

 Bobbins. Stem 2 — 4f high, branching, smooth. Leaves bipinnately dissected, 

 nearly smooth. Heads of flowers on long peduncles, each with 3—4 (or 0) ob- 

 Bcure, obovate, yellow rays. Jl. — Sept. 



* * Rays conspicuous. 



5. B. CHRYSANTHEMOiDES. Radiate Burr-Marigold. 



Fls. radiate ; rays 3 times as long as the nearly equal involucre ; lvs. ob- 

 long, attenuate at each end, connate at base, dentate. — (T) A low plant, with 

 large, yellow-rayed flowers, in muddy places. Can. and U. S. Stem 6 — 20' 

 high, round and smooth. Leaves smooth, with few remote teeth, narrow, oppo- 

 site, with narrow, connate bases. Flowers commonly erect, rays about 8, large, 

 spreading. Scarcely distinct from B. cernua. Sept. Oct. 



6. B. Beckh. Torr. Beckh Burr-Marigold. 



St. subsimple ; submersed lvs. capillaceous-multifid ; emersed ones lanceo- 

 late, connate, acutely serrate or laciniate ; fls. radiate ; rays, longer than the 

 involucre. — % In water, N. Y. Sartwell, &c. Vt. Cliandhr, N. to Can. Stem 

 2 — 3f long, simple or with minute, slender branches above. Lower leaves dis- 

 sected as • in Ranunculus aquatilis ; upper 1—2' long, i as wide, deeply serrate. 

 Head solitary, terminal, yellow. July. Aug. 



