Geothallus is a monotypic genus of liverwort in the family Sphaerocarpaceae family. It includes only the single species Geothallus tuberosus. Its common name is Campbell's liverwort. It is endemic to California, where it is known only from San Diego and Riverside Counties. This liverwort grows in moist coastal scrub habitat and vernal pools. At least one population occurs on the grounds of Marine Corps Base Camp Pendleton, and it has also been noted on the Santa Rosa Plateau.