COMPOSITAE. 1003 



divided into 5-7 lanceolate, acuminate, sharply serrate, incised or nearly entire, 

 sessile or short-stalkecl segments; upper leaves sessile or nearly so, 3-lobed, 3- 

 divided, or entire and linear-lanceolate; heads numerous, 4-6 cm. broad, long- 

 peduncled ; involucre hemispheric, its outer bracts linear or spatulate, sometimes 

 ciliate, about the length of the broader inner ones; rays 6-19. obtuse, golden yellow, 

 14-25 mm. long; achenes 6-8 mm. long; pappus of 2 upwardly hispid teeth or short 

 awns. In swamps and wet meadows, Mass, to Ga,, 111. and Ky. Aug. -Oct. 



Bidens trichosperma tenuiloba (A. Gray) Britton. Segments of the leaves linear- 

 lanceolate, serrate or entire; achenes sometimes smaller. In bogs, 111., Ind., Minn., Iowa 

 and southern Ont. A similar form occurs in southern N. J. 



14. Bidens aristosa (Michx.) Britton. WESTERN TICKSEED-SUNFLOWER- 

 (I. F. f. 3948.) Annual or biennial; stem much branched, 3-9 dm. high. Leaves 

 thin, slender-petioled, pubescent beneath, the lower ones pinnately 5-y-divided, 

 7-15 cm. long, the segments lanceolate, serrate, incised or pinnatifid, acuminate, 

 narrowed at the base; upper leaves less divided, lanceolate, or merely lobed, sessile 

 or short- petioled ; heads numerous, slender-peduncled, 2-5 cm. broad; outer bracts 

 of the hemispheric involucre linear or spatulate; rays 6-g, obtuse; achenes upwardly 

 ciliate and strigose-pubescent; pappus of 2 slender upwardly or downwardly barbed 

 awns, nearly as long as the achene, rarely wanting. In swamps and wet prairies, 

 Del. to Mich., La. and Mo. Aug.-Oct. 



15. Bidens involucrata (Nutt.) Britton. LONG-BRACTED TICKSEED-SUN- 

 FLOWER. (I. F. f. 3949.) Similar to the two preceding species, minutely pubes- 

 cent, 3-9 dm. high, much branched. Segments of the leaves narrower, linear- 

 lanceolate, incised or pinnatifid, long-acuminate; heads numerous, 35 cm. broad, 

 on slender, usually hispid peduncles ; outer bracts of the hemispheric involucre linear- 

 lanceolate, acuminate; rays orange at the base; achenes flat, ciliate and strigose; 

 pappus of 2 short teeth. In swamps, 111. to Kans. , Ark. and Tex. July-Sept. 



1 6. Bidens Beckii Torr. WATER MARIGOLD. (I. F. f. 3950.) Perennial, 

 aquatic; stems simple, or little branched, 6-25 dm. long. Submersed leaves sessile, 

 3-5 cm. long; emersed leaves few, sessile, opposite, or sometimes in 3's, lanceolate 

 or oblong, acute, serrate or laciniate, 1-4 cm. long ; heads solitary or few, short - 

 peduncled, 2.5-3.5 cm. broad; involucre hemispheric, its bracts oval or oblong, ob- 

 tusish, glabrous, the outer somewhat shorter than the inner; rays 6-10, obovate, 

 or oblong, obtuse, golden yellow; achenes nearly terete, each end truncate; pappus 

 of 36 slender awns, downwardly barbed above, smooth below, divergent, 12-25 

 mm. long. In ponds and streams, Quebec to N. J., west to Manitoba and Mo. 

 Aug-Sept. Emersed leaves sometimes wanting. This and a northwestern species 

 constitute the recently-described genus Megalodonta Greene. 



68. THELESPERMA Less. 



Glabrous herbs, with opposite linear and undivided, or finely dissected leaves, 

 and long-peduncled heads of both tubular and radiate flowers, or the rays wanting. 

 Involucre of 2 distinct series of bracts, the outer short, narrow and somewhat 

 spreading, the inner united into a cup, their tips scarious-margined. Receptacle 

 flat, chaffy, the 2-nerved broad white scarious chaff subtending the disk-flowers and 

 achenes. Ray-flowers, when present, neutral, the rays yellow, entire or toothed. 

 Disk-flowers perfect, fertile, their corolla with a slender tube and 5 -toothed limb. 

 Anthers obtuse and entire at the base. Style-tips acute. Achenes, some or all of 

 them, papillose on the back, oblong or linear, slightly compressed or terete, wing- 

 less. Pappus of 2 retrorsely hispid awns or scales, or sometimes none. [Greek, 

 nipple-seed.] About 7 species, natives of the south central U. S., Mex. and south- 

 ern S. Am. 



Rays large ; pappus-awns shorter than the width of the achene. 



Leaves not rigid, their segments filiform-linear ; annual or biennial. 



i. T.trifidum. 



Leaves rigid, their segments linear ; perennial. 2. T. intermedium* 



Rays inconspicuous, or none ; awns longer than the width of the achene. 



3. T. gracile. 



i. Thelespcrma trifidum (Poir.) Britton. FINE-LEAVED THELESPERMA, 

 (I. F. f. 3951.) Stem branched, 3-9 dm. high. Leaves numerous, 4-5 cm. long, 



