8.
Bidens pilosa
Linnaeus, Sp. Pl. 2: 832. 1753.
Bident poilu
Bidens alba
(Linnaeus) de Candolle;
B. alba
var.
radiata
(Schultz-Bipontinus) R. E. Ballard;
B. odorata
Cavanilles;
B. pilosa
var.
radiata
(Schultz-Bipontinus) Schultz-Bipontinus
Annuals
[perennials], (10—)30—60(—180+)[—250] cm.
Leaves:
petioles 10—30(—70) mm; blades either ovate to lanceolate, 30—70(—120) × 12—18(—45) mm, or 1-pinnately lobed, primary lobes 3—7, ovate to lanceolate [linear], (10—)25—80+ × (5—)10—40+ mm [blades 2(—3)-pinnatisect], bases truncate to cuneate, ultimate margins serrate or entire, usually ciliate, apices acute to attenuate, faces pilosulous to sparsely hirtellous or glabrate.
Heads
usually borne singly, sometimes in open, ± corymbiform arrays.
Peduncles
10—20(—90) mm.
Calyculi
(6—)7—9(—13) ± appressed, spatulate to linear bractlets (3—)4—5 mm, margins ciliate, abaxial faces usually hispidulous to puberulent.
Involucres
turbinate to campanulate, 5—6 × (6—)7—8 mm.
Phyllaries
(7—)8—9(—13), lanceolate to oblanceolate, 4—6 mm.
Ray florets
0 or (3—)5—8+; laminae whitish to pinkish [yellowish], 2—3 or 7—15+ mm.
Disc florets
20—40(—80+); corollas yellowish, (2—)3—5 mm.
Cypselae:
outer red-brown, ± flat, linear to narrowly cuneate, (3—)4—5+ mm, margins antrorsely hispidulous, apices ± truncate or somewhat attenuate, faces obscurely 2-grooved, sometimes tuberculate-hispidulous; inner blackish, ± equally 4-angled, linear-fusiform, 7—16 mm, margins antrorsely hispidulous, apices ± attenuate, faces 2-grooved, tuberculate-hispidulous to sparsely strigillose;
pappi
0, or of 2—3(—5), erect to divergent, retrorsely barbed awns (0.5—)2—4 mm.
2
n
= 24, 36, 48, 72.
Flowering year round. Disturbed, wettish sites; 10—1900 m; Ont. Que.; Ala., Ariz., Calif., Conn., Fla., Ga., Ky., La., Md., Mass., Miss., Mo., N.Mex., N.C., Pa., S.C., Tex.; Mexico; Central America; introduced, Europe.
R. Ballard (1986) adopted a narrower circumscription of
Bidens pilosa
than that used here. He used:
B. pilosa
for plants with outer phyllaries 7—10, ray florets usually 0 (when present, laminae 2—3 mm), disc florets 35—75, pappi of 3(—5) awns 1—3 mm, and 2
n
= 72;
B. alba
for plants with outer phyllaries (8—)12(—16), ray florets 5—8 (laminae 5—16 mm), pappi of 2 awns 1—2 mm, and 2
n
= 48; and
B. odorata
for plants with outer phyllaries (6—)8(—12), ray florets 5—8 (laminae 3—18 mm), disc florets 12—61, pappi 0, or of 1—2 awns 1—3 mm, and 2
n
= 24.
SELECTED REFERENCE
Ballard, R. 1986.
Bidens pilosa
complex (Asteraceae) in North and Central America. Amer. J. Bot. 73: 1452—1465.
