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Bidens L.


Bidens tripartita

Credit: HAST

Annual or perennial herbs, rarely shrubs. Stems erect. Leaves opposite or rarely whorled, compound, lobed, or simple leaves. Heads solitary, in corymbs or panicles, radiate or discoid. Outer florets ligulate, neuter or pistillate, usually yellow; central florets perfect or rarely functional staminate, (4-)5-lobed, yellow or brownish orange. Achenes linear-oblong to ellipsoid, 3- or 4-angled or compressed, sometimes winged. Pappus of up to four usually barbed awns and/or bristles, or absent.

About 240 species distributed worldwidely, especially North and South America; four species, one of which is represented by three varieties, in Taiwan.

Sherff, E. E. 1937. The Genus Bidens, parts I & II. Field. Mus. Nat. Hist., Bot. Ser. 16: 1-709.


1 Achenes ovate-cuneate, 2-2.5 mm wide, compressed, glabrous but retrorsely spinulose on margins and ribs.   Bidens tripartita
+ Achenes linear, 1-1.5 mm wide, tetragonous, more or less strigose.   (2)
2 (1) Involucral bracts linear, not dilated toward apex; achenes fewer than 50.   (3)
+ Involucral bracts spatulate, dilated toward apex; achenes numerous, ca. 50-70.   (4)
3 (2) Leaves 2-3 pinnatisect, leaflet lanceolate, terminal segment narrow, few-toothed.   Bidens bipinnata
+ Leaves subpinnately parted, leaflet deltoid-ovate, terminal segment broad, ovate, distinctly toothed.   Bidens biternata
4 (2) Heads discoid.   var. radiata
+ Heads radiate.   (5)
5 (4) Ray florets usually shorter than 8 mm.   var. minor
+ Ray florets usually longer than 10 mm.   var. radiata

Lower Taxa

Related Synonym(s):


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