Kim, Seung-Chul, Daniel J. Crawford, Mesfin Tadesse, Mary Berbee, Fred R. Ganders, Mona Pirseyedi, and Elizabeth J. Esselman (September–July 1999). ITS sequences and phylogenetic relationships in Bidens and Coreopsis (Asteraceae). Systematic Botany24 (3): 480–493. DOI: 10.2307/2419701.