- Kingdom: Plantae
- Phylum: Rhodophyta
- Class: Florideophyceae
- Order: Corallinales
- Family: Hapalidiaceae
- Scientific name: Phymatolithon lenormandii
- Norwegian: slettrugl
It forms a thin crust, not more than 0,6 mm thick. The color is pink with smooth, white or yellow margins. Similar, but not so abundant species are Lithophyllum incrustans and L. orbiculatum.
Abundant on any hard substrate in the tidal zone.
It is known on both sides of the North Atlantic Ocean, as far south as the Azores.