Stevenson, D.W. (1981). «Observations on ptyxis, phenology, and trichomes in the Cycadales and their systematic implications». American Journal of Botany. 68 (8): 1104–14. doi:10.1002/j.1537-2197.1981.tb06394.x
Christenhusz, M.J.M.; Reveal, J.L.; Farjon, A.K.; Gardner, M.F.; Mill, R.R.; Chase, M.W. (2011). «A new classification and linear sequence of extant gymnosperms». Phytotaxa. 19: 55–70. doi:10.11646/phytotaxa.19.1.3
Hill, K.D.; Stevenson, D.W. (1999). «A world list of Cycads». Excelsa (Journal of the Aloe, Cactus and Succulent Society of Zimbabwe). 19: 67–72. ISSN0301-441X. OCLC612375682