An unusual new species of Bidens (Asteraceae) from Brazil is described and its placement within the genus is elucidated by phylogenetic analysis of ITS sequences. The new species, described as Bidens campanulata, is distinct in the genus based on its broadly campanulate corolla limb with long lobes, an extremely reduced involucre (shorter than the flower length), and the absence of awns on the pappus. This study presents a taxonomic treatment of the species of Bidens with discoid capitula endemic to the Brazilian Cerrado, including a key to the species, typification, and information on conservation status.