7.
Bidens bipinnata
Linnaeus, Sp. Pl. 2: 832. 1753.
Bidens bipinnata
var.
biternatoides
Sherff
Annuals,
(15—)30—100(—150+) cm.
Leaves:
petioles 20—50 mm; blades rounded-deltate to ovate or lanceolate overall, (20—)30—70+ × (20—)30—60+ mm, (1—)2(—3)-pinnatisect, ultimate lobes obovate or lanceolate, 15—45+ × 10—25+ mm, bases truncate to cuneate, ultimate margins entire, sometimes ciliolate, apices rounded to acute or attenuate, faces usually glabrous, sometimes hirtellous.
Heads
usually borne singly, sometimes in ± corymbiform arrays.
Peduncles
(10—)20—50(—100) mm.
Calyculi
of (7—)8(—10) linear bractlets 3—5 mm, ± appressed, margins ciliate, abaxial faces usually glabrous.
Involucres
± campanulate, 5—7 × 3—4(—5) mm.
Phyllaries
8—12, lanceolate to linear, 4—6 mm.
Ray florets
0 or 3—5+; laminae yellowish or whitish, 1—2(—3) mm.
Disc florets
10—20(—30+); corollas yellowish to whitish, 2—3 mm.
Cypselae
red-brown, outer weakly obcompressed, 7—15 mm, inner ± 4-angled, linear to linear-fusiform, 12—18 mm, margins not ciliate, apices ± attenuate, faces 2-grooved, often tuberculate-hispidulous;
pappi
of (2—)3—4, erect to divergent, retrorsely barbed awns 2—4 mm.
2
n
= 24, 72.
Flowering (Jun—)Aug—Sep(—Oct). Fields, forests, disturbed, wettish sites; 10—1800 m; N.B., Ont.; Ala., Ariz., Ark., Conn., D.C., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., La., Md., Miss., Mo., Nebr., N.J., N.Mex., N.Y., N.C., Ohio, Okla., Pa., R.I., S.C., Tenn., Tex., Va., W.Va.; South America; Europe; Asia; Pacific Islands.
Bidens bipinnata
is probably native in eastern Asia and introduced in South America, Europe, Asia, and Pacific Islands.
