COMPOSITE FAMILY. 



183 



13. BI'DENS, L. BUR-MAEIGOLD. 



[Latin, Bi-dens, having 2 teeth ; in allusion to the awns of the akenes.] 



Heads many-flowered ; ray-Jlorets neutral, often inconspicuous and some- 

 times wanting, — those of the disk tubular and perfect. Involucre 

 double, — the outer scales larger and often foliaceous. Receptacle flat- 

 tish, — the chaff deciduous with the fruit. Akenes flattened, or slender 

 and more or less 4-sided, crowned with two or more retrorsely hispid 

 awns. Annual or sometimes perennial herbs. Leaves opposite, incised- 

 serrate or pinnatifidly dissected. Flcwers mostly yellow. 

 * Akenes flat and broadish, not beaked at summit, ciliate on the margins. 



1. B. frondo'sa, L. Leaves odd-pinnately divided, — the lower ones 

 with 5 divisions, the upper with 3 ; divisions distinct and mostly peti- 

 olulate, lanceolate, serrate ; heads discoid, on slender axillary peduncles ; 

 outer scales of the involucre foliaceous, narrowed and ciliate at base, 

 much longer than the head ; akenes obovate-cuneate, 2-awned, pubescent 

 and ciliate with erect hairs. 



Frondose Bidens. Bur-marigold. 



Root annual. Stem 2-4 or 5 feet high, somewhat hairy, often dark purple, branched. 

 Leaflets or segments 2-4 or 5 inches long, pilose beneath, abruptly narrowed at base to a 

 short margined ciliate pefiolule, — the common petiole 1-3 inches long. Heads rather small, 

 on long slender naked peduncles. Involucre double, — the 8-10 outer scales lanceolate, 

 leaf-like, unequal, 2 or 3-5 or 6 times as long as the head, ovate-lanceolate, with a scarious 

 margin. Florets yellowish. Chaff of the receptacle linear-lanceolate, about as long as 

 the akenes. 



Gardens, fence-rows, Indian-corn fields, &c. : throughout the United States. Fl. Au- 

 gust-September. Fr. October. 



Obs. All the species, here enumerated, are very worthless, and par- 

 ticularly disagreeable weeds, — on account of the barbed awns of the 

 fruit, which cause it to adhere in great numbers to clothing. This one 

 is apt to be quite abundant in gardens, Indian-corn fields, &c. and if 

 permitted to mature its fruit, becomes very annoying, in the latter part 

 of summer. 



2. B. chrysanthemoi'des, Mx. Leaves oblong-lanceolate, tapering 

 at each end, serrate, sessile, and connate at base ; heads conspicuously 

 radiate, often somewhat nodding ; outer scales of the involucre foliaceous, 

 mostly shorter than the rays ; akenes oblong-cuneate, 2 - 4-awned, re- 

 trorsely aculeate-ciliate on the margins. 



Chrysanthemum-like Bidens. Beggar-ticks. 



Plant glabrous. i?ooi annual. Stem 6 inches to 2 feet high, erect or often declined at 

 base, branching, the branches opposite and axillary. Leaves 3-6 inches long. Heads 

 rather large, solitary, terminating the branches. Outer scales of the involucre about 8, 

 hnear-lanceolate, ciliate-serrulate, spreading, the largest sometimes- nearly as long as the 

 rays ; the inner scales membranaceous, elliptic or ovate-oblong, nearly equal, about as 

 long as the disk-florets. iZays bright yellow, numerous, near an inch long. ATcenes striate- 

 ribbed and somewhat keeled on the flatted sides ; aums usually 4. Chaff' of the receptacle 

 spatulate-linear, scarious, 3-nerved, yellow, or sometimes purplish at summit. 



Low grounds, along swampy rivulets : generally throughout the United States. Fl. 

 August -September. Fr. October. 



Obs. This species is rather showy, when in flower, — and is less inclined 

 than either the preceding or the following to invade cultivated grounds 



