Mabberley, D.J. 2008: Mabberley's plant book, a portable dictionary of plants, their classification and uses. Edition 3. Cambridge University Press.
Salisbury, R.A. 1807: Observations on the genera of Trollius, Eranthis, Helleborus, Coptis, and Isopyrum. Transactions of the Linnean Society of London 8: 300–307.