N. K. B.  Robson, ?Studies in the genus Hypericum L. (Guttiferae) 4(2). Section 9. Hypericum sensu lato (part 2): subsection 1. Hypericum series 1. Hypericum.?, Bull. Nat. Hist. Mus. (London), Bot., vol. 32, pp. 61-123 (2002) - illus., 2002.