206 | Rhodora [OcroBER 
BIDENS CERNUA IN EASTERN AMERICA. Bidens cernua L. is a 
highly variable species with several well defined varieties in north- 
eastern America. It belongs to a group of three species with simple 
leaves and achenes with a convex cartilaginous summit. These three 
species may be distinguished as follows. 
Mature disk (except in depauperate extremes) 1.3-2.8 em. 
broad: fruiting heads often nodding: outer involucre 
reflexed, spreading or merely subascending:  disk- 
corollas 4-5 mm. long, 5-toothed: anthers exserted, 
purple-black: achenes not conspicuously striate between 
the margins and midribs or keels; the central 1.8-2.5 
mm. broad. 
Achenes straight and flat, not winged nor strongly keeled, 
deep-brown or purplish; the outer 6-8 mm. long, with 
marginal awns 2.8-4.5 mm. long; the central 8-9.5 
mm. long, with marginal awns 3.5-5 mm. long: stem 
firm and usually smooth; its rooting base up to 6 dm. 
long: outer involucre rarely longer than the inner: 
chaff reddish-tipped: rays 1.5-3 em. long.............. ... B. laevis. 
Achenes curved, with almost wing-like pale margins and 
keels, olivaceous; the outer 3.3-6.3 mm. long, with 
marginal awns 2-2.8 mm. long; the central 4.2-7.8 
mm. long, with marginal awns 2.6-4 mm. long: stem 
soft and usually somewhat hispid; its rooting base 
rarely 1 dm. long: outer involucre mostly longer than 
the mner: chaff yellow-tipped: rays wanting or at 
most: L7 e "SEENEN TH 
Mature disk rarely 1.5 em. broad: fruiting heads erect: outer 
involucre ascending: disk-corollas 3.5-4 mm. long, 4- 
toothed: anthers included, pale: achenes distinctly 7-15- 
striate on each face; the central 1.4-1.9 mm. broad, flat, 
olive-broim OF GES oo. ew cw ANA cw e y noni B. hyperborea. 
Bidens laevis is not specially variable with us; the variations of 
B. hyperborea have recently been discussed; and to round out the 
treatment of this group the northeastern varieties of B. cernua are 
here considered. Our variations of this species are as follows. 
Stems stoutish, 0.25-1 cm. in diameter at base, commonly 
branching, 0.5-1.8 m. high: leaves sessile or at most 
narrowed at base, thickish, 0.2-2 dm. long; heads com- 
monly numerous, broadly hemispherical, many-flowered ; 
the primary ones with disks 1-2.7 em. broad, nodding 
in fruit: outer involucre of 5-10 bracts; inner of about 
8 bracts 6-12 mm. long. 
Leaves tapering to long acuminate-attenuate tips; the 
primary with 4-24 pairs of sharp serrations: bracts 
of outer involucre linear to lanceolate, acute or 
acutish. 
Leaves with broad connate or subconnate bases, scarcely 
narrowed below the middle. 
Leaves linear to oblanceolate, with 4-13 pairs of 
coarse teeth 1-5 mm. high................ B. cernua (typical). 
1 RHODORA, xx. 146-150 (1918). 
