Mankyua chejuense, a fern endemic to Cheju Island, Republic of Korea, which lies 120 km south of the Korean Peninsula, appears to be restricted to five extant subpopulations in the north-east of the Island, with a total population of c. 1,300 individuals. Major threats to the existence of the species include shifting cultivation, plantation, overuse of basaltic rocks that are part of the species' microhabitat, farming and pasturage, and the construction of roads and golf courses in lowland areas. The information currently available for the species indicates that it should be categorized as Critically Endangered on the IUCN Red List. For conservation of the species it needs to be included on the national threatened species list, and its habitat designated as an ecological reserve. Intensive surveys are required in order to establish whether there are any other extant subpopulations of the species, and the presently known subpopulations require long-term monitoring and continuous protection.