COMPOSITE. (COMPOSITE FAMILY.) 261 



42. 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. Achenia flattened 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.) 



* Achenia flat, not tapering at the summit. (All annuals ?) 



1. B. frondbsa, L. (COMMON BEGGAR-TICKS.) Smooth or rather hairy, 

 tall (2 -6 high) and branching; leaves 3 - 5-divided ; the leaflets mostly stalked, 

 lanceolate, pointed, coarsely toothed ; outer leafy involucre much longer than 

 the head, ciliate below ; rays none or few and very small ; achenia wedge-obovate, 

 2-awned, the margins ciliate with upwardly-turned bristles, except near the summit. 

 Moist waste places : a coarse troublesome weed, the achenia, as in the other 

 species, adhering by their retrorsely barbed awns to the dress, and to the fleece 

 of animals. July - Oct. 



2. B. connata, Muhl. (SWAMP BEGGAR-TICKS.) Smooth (l-2 high) ; 

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

 gined petioles which are slightly united at the base ; the lower often 3-divided, their 

 lateral divisions united at the base and decurrent on the petiole ; scales of the outer 

 involucre longer than the head, few, mostly obtuse ; rays none ; achenia narrowly 

 wedge-form, 3- (2-4-) awned, the margins minutely retrorsely ciliate. (B. tripartita, 

 Bigel.) A thin-leaved more petioled form is B. petiolata, Nutt. E. New Eng- 

 land to Illinois, and southward. Var. COM6SA is stouter, the leaves commonly 

 all simple, upper ones nearly sessile, the heads larger and with more numerous 

 and leafy bracts. Illinois, Kentucky, and westward. Aug. -Oct. 



3. B. cernua, L. (SMALLER BUR-MARIGOLD.) Nearly smooth (5'- 10' 

 high); leaves all undivided, lanceolate, unequally serrate, scarcely connate; heads 

 nodding, with or without (light yellow) rays: outer involucre longer than the 

 head; achenia wedge-obovate, 4-awned, the margins downwardly barbed. 

 Wet places, Virginia to Wisconsin, and northward. July - Sept. Rays, when 

 present, smaller than in the next, the leaves irregularly toothed, and the outer 

 involucre more leaf-like. (Eu.) 



4. B. Chrysanthemoides, Michx. (LARGER BUR-MARIGOLD.) Smooth, 

 erect, or reclining at the base (6' -30' high) ; leaves lanceolate, tapering at both 

 ends, more or less connate, regularly serrate ; outer involucre mostly shorter than 

 the showy golden-yellow (!' long) rays; achenia wedge-shaped, with almost prickly 

 downwardly barbed margins.; awns 2, 3, or 4. Swamps : common. Aug.' - 

 Oct. Northward it runs into No. 3. 



* * Achenia linear or awl-shaped, 4-sided, slender, tapering at the summit. 



5. B. B6ckii, Torr. (WATER MARIGOLD.) Aquatic, perhaps perennial, 

 smooth ; stems long and slender, bearing crowded immersed leaves many times dis- 

 sected into fine capillary divisions ; the few emerging leaves lanceolate, slightly 

 connate, toothed ; heads single, short-peduncled ; involucre much shorter than the 

 showy (golden yellow) rays; achenia linear, thickish, smooth (j' long), bearing 4- 

 6 stout divergent awns which are an inch long and barbed only towards the 



