Karakiev, T., and R. Tzonev. “Saxifrago Ferdinandi-Coburgi-Seslerietum Actarovii – a New Association from the Subalpine Belt of the Slavianka (Orvilos) Mts. (Bulgaria )”. Hacquetia, vol. 10, no. 1, Aug. 2015, doi:10.2478/v10028-011-0004-8 .