W. T.  Stearn, A synopsis of the genus Vinca including its taxonomic and nomenclatural history. New York, 1973, pp. 19 - 94.

W. T.  Stearn, ?Epimedium and Vancouveria (Berberidaceae), a monograph?, J. Linn. Bot. Soc, vol. 51, pp. 409 - 535, 1938.