N.Robson (Ledeb. ex Rchb.) 2002 - Robson NKb. (2002) Studies in the genus Hypericum L. (Guttiferae) 4(2). Section 9. Hypericum sensu lato (part 2): subsection 1. Hypericum series 1. Hypericum. Bulletin of The Natural History Museum. Botany Series 32(02):. doi: 10.1017/S096804460200004X.
There is no corrections for Hypericum perforatum subsp. songaricum yet.