In moist soil near and along streams, springs and ditches, s. Ariz. (Cochise, 

 Santa Cruz and Pima cos.) to Guat., spring-autumn. 



3. Bidens cernua L. Fig. 768. 



Annual; stems erect or ascending, 1-10 dm. tall, occasionally somewhat succu- 

 lent, glabrous to scabrous-hispid; leaves normally opposite, sometimes verticillate, 

 linear-lanceolate or lanceolate, unequally serrate, narrowed to sessile or subsessile, 

 with connate base, 4-17 cm. long; heads at first erect, becoming nodding, radiate 

 or discoid, in anthesis 1-5 cm. wide, 6-12 mm. high; outer phyllaries 5 to 8, 

 foliaceous, linear-lanceolate, sparsely acicular-ciliate or glabrous, unequal in 

 length, usually longer than the disk flowers (to 4 cm. long), the inner phyllaries 

 membranous, striate, orange-brown, ovate-lanceolate to obovate-lanceolate, 

 scarcely longer than the disk flowers; receptacle bracts similar but narrower; ray 

 flowers when present 6 to 8, ovate-lanceolate, 10-15 (-20) mm. long, about 1 to 

 2 times as long as the disk; achenes often purplish, normally cuneate and apically 

 thickened, marginal and median angles mostly prominent and usually strongly 

 callous-thickened, the body thus more or less 4-angled and quadrate in cross 

 section (at least subapically), 5-6.5 mm. long, retrorsely hispid (especially on 

 angles); awns 4 (sometimes only 2 or 3), usually 1 at each angle of achene apex, 

 3^ mm. long, retrorsely barbed. 



Marshy ground, wet lowlands and along sloughs, in Okla. (Alfalfa Co.) and 

 N.M. (Colfax and Rio Arriba cos.), June-Oct.; N.B. to B.C., s. to N.C., Okla., 

 N.M. and Calif.; widespread in Old World. 



4. Bidens mitis (Michx.) Sherff. Fig. 769. 



Annual herb, more or less glabrous, 3-10 dm. tall; leaves petiolate (petioles 

 3-30 mm. long), including the petioles 4-12 cm. long, membranous, variable, 

 lanceolate or ovate, serrate, acute or acuminate, sometimes entire or more often 

 pinnately 3- to 7-parted, the terminal leaflet commonly very elongate, the blade 

 or segments linear and commonly entire or broader and incised-serrate, very rarely 

 decompound; peduncles 2-12 cm. long; heads 2-5 cm. broad; involucre glabrous or 

 sparsely hispid at the base; outer phyllaries 7 to 10, linear or linear-spatulate, 

 usually ciliate, acute or obtuse, 5-10 mm. long, the inner phyllaries often shorter; 

 rays about 8, golden-yellow, 12-27 mm. long, oblanceolate or elliptic-obovate, 

 entire or very minutely denticulate; achenes flattish or scarcely trigonal in tran- 

 section, broadly cuneate, black, the body 2.5-4.5 mm. long; pappus awns 0.6-1 

 mm. long, antrorsely setose. 



Rare in wet places, especially brackish or fresh-water swamps, in s.e. Tex., 

 in moist soil, spring-early summer; s.e. U.S. (Md. to Tex.). 



5. Bidens aristosa (Michx.) Britt. Tickseed sunflower. 



Annual or biennial herb, glabrate or scarcely pubescent, 3-10 (-15) dm. tall; 

 leaves petiolate [petioles 10-15 (-30) mm. long], including the petiole 5-15 cm. 

 long, pinnate or bipinnate; blade segments lanceolate or linear-lanceolate, acumi- 

 nate, incised-serrate or pinnatifid, membranous, ciliate, scarcely pubescent on the 

 lower surface; heads 2-5 cm. broad, 7-9 mm. high; involucre often hispid; 

 phyllaries subequal, the outer ones 8 to 10, linear, sometimes scarcely ciliate, 

 sometimes very ciliate, 5-12 mm. long; rays 6 to 10, golden, 10-25 mm. long, 

 oblong-oblanceolate, apically obtuse and entire or subdenticulate; achenes to 6.5 

 mm. long, flat or flattish, blackish or yellowish-black; pappus awns rarely absent 

 (var. mutica Gray), usually present and smooth or antrorsely ciliate. 



In moist or seasonally moist soil, e. and s.e. Tex., infrequent, spring-early 

 summer; most of the e. U.S. 



1667 



