ORDER LXVIII. COMPOSITE. 395 



Genus LIV.— BI'DENS. L. 

 (From bidens, two teeth, from the two awns of the fruit) 



Involucre double, the outer unequal ; ray florets neutral when 

 present, frequently wanting ; those of the disk perfect. Recep- 

 tacle flat, chaffy ; pappus consisting of 4 retrorsely scabrous 

 awns. Seed quadrangular. 



1. B. chrysanthemoi'des, (Mich.) Stein glabrous below, somewhat 

 pubescent toward the summit, with opposite branches. Leaves sessile, 

 opposite, oblong-lanceolate, serrate, glabrous, somewhat connate ; invo- 

 lucre double, the exterior one consisting of about 8 unequal, foliaceous 

 leaves ; the interior of about the same number of equal, membranace- 

 ous leaves ; ray florets lanceolate, 8. Seed compressed, oblong ; pap- 

 pus consisting of 2 awns which are distinct, and 2 othei'3 very minute; 

 receptacle convex. — Yellow. If. Oct. — Nov. In wet, cultivated 

 lands. 2—3 feet. 



2. B. conna'ta, (Muhl.) Stem glabrous, with opposite branches. 

 Leaves opposite, lanceolate, toothed, glabrous, attenuate at the base ; 

 the lower ones ternate, the upper ones simple, all sessile. Flowers sol- 

 itary, on opposite peduncles; the exterior involucre foliaceous, the in- 

 terior chaffy ; ray florets none. — Yellow. 2f . July — Oct. Middle 

 Car. and Geo. 2 — 3 feet. 



3. B. frondo'sa, (L.) Stem slightly pubescent, branching. Leaves 

 lanceolate ; the lower ones pinnate, the upper ternate and simple, 

 slightly pubescent. Flowers solitary, on opposite and terminal pedun- 

 cles ; exterior involucre with unequal, ciliate scales ; the exterior chaffy ; 

 ray florets none. — Yellow. If. June — Sept. Damp soils. Common. 



4. B. bipinna'ta, (L.) Stem glabrous, obtusely angled, with opposite 

 branches. Leaves opposite, decussate, bipinnate; leaflets lanceolate, 

 pinnatifid, slightly pubescent along the margin. Flowers on long, usu- 

 ally terminal, peduncles ; exterior involucre with linear-lanceolate 

 leaves ; interior leaves ciliate toward the summit. Seed slightly angled. 

 — Yellow. If. July — Oct. Common. 2 — 4 feet. 



Genus LV. — ACMEL'LA. L. (Spilanthes, Jacq.) 

 (From akme, a point.) 



Involucre consisting of 12 leaves, arranged in a double series, 

 pubescent, equal ; florets of the ray pistillate, of the disk per- 

 fect. Seed quadrangular, compressed. Receptacle chaffy, with 

 yellow scales. 



1. A. re'pens, (Pers.) Stem procumbent, rooting at the lower joints, 

 pubescent. Leaves opposite, ovate-lanceolate, attenuate at the base, 

 slightly pubescent. Flowers solitary, on axillary and terminal pedun- 

 cles, leaves of the involucre ovate-lanceolate, acute ; ray florets about 

 12. Seed oblong, naked, truncate at the summit. — Yellow. If. Sept. 

 —Oct. Wet soils. 1—2 feet. 



2. A. NuTTALi/n, (T. <fc G.) Stem pubescent, diffusely branched. 

 Leaves ovate or oblong-ovate, coarsely serrate. Achenia with ciliate 

 margins. — Lou. 



