Cetradonia linearis, commonly known as the rock gnome lichen, is a squamulose lichen found in the higher elevations of the southern Appalachian Mountains. Populations are only known to exist in Georgia, North Carolina, South Carolina and Tennessee. The lichen occurs only in frequent fog, or in deep river gorges. Because of its specialized habitat requirements and heavy collection for scientific purposes, the lichen has been listed as an endangered species since January 18, 1995. It is only one of two lichens on the endangered species list, the other being the Florida perforate cladonia.