The following three
Bidens species are most easily confused.
1. Ray florets absent ........................ Bidens tripartita
1. Ray florets present, yellow ............................. 2
2. Summit of mature achenes convex and cartilaginous, heads nodding, fruiting heads on pressed specimens spherical, leaves strap-like and never deeply three-lobed ........................... Bidens cernua
2. Summit of mature achenes flat or concave, not cartilaginous, heads erect, fruiting heads on pressed specimens hemispherical, leaves not strap-like, often three-lobed.......................................... Bidens amplissima
Source:
Modifed from Ganders, Fred, Rose Klinkenberg and Brian Klinkenberg. 2002. British Columbia loses an endemic species: Bidens amplissima (Asteraceae) also occurs in Washington State. Botanical Electronic News 293.