Natural hybridization between genera that diverged from each other approximately 60 million years ago
The American Naturalist (2015) - Comments
pubmed: 25674696  doi: 10.1086/679662  issn: 1537-5323  issn: 0003-0147 

Carl J. Rothfels, Anne K. Johnson, Peter H. Hovenkamp, David L. Swofford, Harry C. Roskam, Christopher R. Fraser-Jenkins, Michael D. Windham, Kathleen M. Pryer