GENUS 71. 



THISTLE FAMILY. 



499 



12. Bidens aristosa (Michx.) Britton. Western Tickseed-Sunflower. 



Fig. 4516. 



Coreopsis aristosa Michx. Fl. Bor. Am. 2: 140. 1803. 

 C. aristata Muhl. ; Willd. Sp. PI. 3: 2253. 1804. 

 B. aristosa Britton, Bull. Torr. Club 20: 281. 1893. 



Annual or biennial; stem much branched, i-3 

 high. Leaves thin, slender-petioled, pubescent 

 beneath, the lower ones pinnately 5~7-divided, 

 3'-6' long, the segments lanceolate, serrate, in- 

 cised or pinnatifid, acuminate, narrowed at the 

 base; upper leaves less divided, lanceolate, or 

 merely lobed, sessile or short-petioled ; heads nu- 

 merous, slender-peduncled, i'-2' broad; outer 

 bracts of the hemispheric involucre 8-10, linear 

 or spatulate, usually ciliate, not surpassing the 

 inner; rays 6-9, obtuse; achenes very flat, oblan- 

 ceolate or obovate, upwardly ciliate and strigose- 

 pubescent; pappus of 2, rarely 4, slender upward- 

 ly or downwardly barbed awns, sometimes nearly 

 as long as the achene, rarely wanting. 



In swamps and wet prairies, Ohio to Minnesota, 

 south to Louisiana and Missouri; southeastern Penn- 

 sylvania and Delaware. Aug.-Oct. 



13. Bidens involucrata (Nutt.) Britton. 



Long-bracted Tickseed-Sunflower. 



Fig. 45I7- 



Coreopsis involucrata Nutt. Journ. Phil. Acad. 7 : 74. 

 1834- 



Didens inv olucra a Britton, Bull. Torr. Club 20: 281. 

 1893. 



Similar to the two preceding species, minutely 

 pubescent, i-3 high, much branched. Segments 

 of the leaves narrower, linear-lanceolate, incised 

 or pinnatifid, long-acuminate; heads numerous, 

 i '-2' broad, on slender usually hispid peduncles ; 

 outer bracts of the hemispheric involucre 10-20, 

 linear-lanceolate, acuminate, densely hispid and 

 ciliate, much exceeding the inner ones; rays 

 orange at the base; achenes flat, ciliate and stri- 

 gose; pappus of 2 short teeth. 



In swamps, Illinois to Kansas, Arkansas and Texas; 

 southeastern Pennsylvania and Delaware. July-Sept. 



72. MEGALODONTA Greene, Pittonia 4: 270. 1901. 



Perennial aquatic herbs, with opposite or whorled leaves, those of the submersed ones 

 filiformly dissected, those of the emersed ones serrate to laciniate, and solitary peduncled 

 showy heads with both tubular and radiate flowers. Involucre hemispheric, its bracts in 2 

 series, rather broad, distinct or nearly so, the outer ones smaller than the inner, often lax. 

 Receptacle chaffy. Rays neutral, yellow. Disk-flowers perfect, fertile, their corollas tubular, 

 S-toothed. Anthers minutely sagittate at the base. Style-branches with subulate tips. 

 Achenes nearly terete, truncate at both ends. Pappus of 3-6 long-subulate awns which are 

 retrorsely barbed, except near the base. [Greek, large-toothed, referring to the pappus awns.] 



Two known species, the following typical, the other occurring in Washington State. 



