Brackel, W. v. & Berger, F. 2010. Gall-inducing species of Polycoccum (Ascomycota) on the lichen genus Placopsis. — Herzogia 23: 195–204.
Three new gall-inducing species of Polycoccum, all dwelling on hosts of the genus Placopsis, are described: Polycoccum deformans on Placopsis lambii and P. gelida, Polycoccum perrugosae on Placopsis perrugosa, andPolycoccum islandicum on Placopsis gelida. A key to the lichenicolous fungi currently known on Placopsis is presented.