A genus of about 240 species, herbs, cosmopolitan. Recent molecular studies suggest that the relationship between Bidens and Coreopsis is complex, and that changes in taxonomy will be needed to more accurately reflect relationships (Kim et al. 1999; Crawford & Mort 2005).
ID notes:The involucre of phyllaries is subtended by an additional series of bracteal structures, the calyculus.
Ref: Ballard (1986); Crawford & Mort (2005); Cronquist (1980); Kim et al. (1999); Lipscomb & Smith (1977); Roberts (1985); Sherff & Alexander (1955); Strother & Weedon (2006) In Flora of North America Editorial Committee (2006c). Show full citations.