(en) Mark A. Ragan, "A Third Kingdom of Eukaryotic Life: History of an Idea", Archiv für Protistenkunde, Vol.148, No.3, October 1997, p.225-243. DOI10.1016/S0003-9365(97)80004-8
(en) Mark A. Ragan, "Trees and networks before and after Darwin", Biology Direct, Vol.4, No.43, November 16, 2009, p.18. DOI10.1186/1745-6150-4-43