284 COMPOSITE. (COMPOSITE 



16. C. involucrata, Nutt. Heads rather larger, the outer scales 12 ~ 20, 

 mostly exceeding the inner, slender and hispid ; achenes with 2 short acute 

 teeth. W. 111. to Kan. and Tex. 



H- -H- Rays none, or rarely rudimentary ; outer scales usually 3-5, loose, leafy, 

 commonly surpassing the short-pedunculate heads ; achenes narrowly cune- 

 ate ; plants glabrous, 1-3 high ; leaves petiolate. 



17. C. bidentoides, Nutt. Paniculately branched; leaves undivided, 

 lanceolate, coarsely toothed, tapering at both ends ; heads 6-10" long ; achenes 

 nearly subulate, bearing a pair of very slender upwardly roughened awns sur- 

 passing the corolla (4" long), but shorter than the achene, often also 2 minute 

 teeth alternate with the awns. Shores of Delaware River, near Philad., and 

 Delaware Bay, to Md. Hybridizes with Bidens frondosa. 



18. C. discoidea, Torr. & Gray. Diffusely branched, 1 - 2 high ; leaves 

 ternately divided, slender-petioled ; leaflets ovate-lanceolate, pointed, coarsely 

 serrate; heads 2 - 3" long ; achenes linear-wedge-shaped (2 -3" lor g), bearing 

 a pair of short and stout upwardly-barbed awns of the length of the corolla. 

 Wet banks and swamps, Conn, to Ohio, 111., and southward. July. 



56. BIDENS, L. BUR-MARIGOLD. 



Heads many-flowered ; the rays when present 3-8, neutral. Involucre double, 

 the outer commonly large and foliaceous. Receptacle flattish ; the chaff decidu- 

 ous with the fruit. Achenes flattered parallel with the scales of the involucre, 

 or slender and 4-sided, crowned with 2 or more rigid and persistent awns which 

 are downwardly barbed. Annual or perennial herbs, with opposite various 

 leaves, and mostly yellow flowers. (Latin, bidens, two-toothed.) 



# Achenes flat, not tapering at the summit; outer involucre foliaceous ; annuals, 

 - Heads erect, nearly rayless ; leaves mostly petiolate. 



1. B. frond6sa, L. (COMMON BEGGAR-TICKS. STICK-TIGHT.) Smooth 

 or rather hairy, tall (2-6 high), branching; leaves 3-5-divided; leaflet* 

 mostly stalked, lanceolate, pointed, coarsely toothed; outer involucre much 

 longer than the head, ciliate below ; achenes wedge-obovate, 2-awned, ciliate (thft 

 bristles ascending except near the summit). Moist waste places ; a coarse 

 troublesome weed, the achenes, as in the other species, adhering to clothing, 

 etc., by their retrorsely barbed awns. Hybrids occur with Coreopsis aristosa 

 and other species. July - Oct. 



2. B. COnnata, Muhl. (SWAMP BEGGAR-TICKS.) Smooth ( 1-2 high); 

 leaves lanceolate or oblong-lanceolate, pointed, sharply serrate, tapering into 

 margined slightly united petioles; the lower often ^-divided, their lateral divi- 

 sions united at the base and decurrent on the petiole ; outer scales longer than 

 the head, few, mostly obtuse ; rays none ; achenes narrowly wedge-form, 3- (2 - 

 4-) awned, the margins minutely retrorsely ciliate. E. New Eng. to Minn., and 

 iouthward. Var. COM6SA, Gray, is stouter, the leaves commonly all simple, 

 upper ones nearly sessile, the heads larger and with very leafy involucre. 111., 

 Ky., and westward. Aug. - Oct. Var. PINNATA, Watson ; leaves nearly all 

 pinnately divided, the 5-7 narrow divisions sparingly incised ; achenes 4-awned. 

 Hennepin Co., Minn. (F. L. Couillard). 



