Soltis, D. E. et alii. (28 authors). 2011. "Angiosperm phylogeny: 17 genes, 640 taxa". American Journal of Botany98(4):704-730. doi:10.3732/ajb.1000404
Cronk Q. C. B., Needham I., and Rudall P. J. 2015. Evolution of catkins: inflorescence morphology of selected Salicaceae in an evolutionary and developmental context. Frontiers in Plant Science. 2015; 6: 1030. doi:10.3389/fpls.2015.01030