Coenogonium lueckingii, a new corticolous species characterized by a greenish-gray thallus with a white prothallus and 1-septate fusiform ascospores, is described from South Korea. A description of the species is provided together with notes on its chemistry, distribution, ecology and taxonomy. Possible related lichen taxa are discussed briefly, and a worldwide key to the crustose Coenogonium species having a prothallus is also provided. Besides this, Coenogonium pineti is also reported for the first time for the lichen flora of South Korea. Biodiversity, Chuja Island, Jeju Island, taxonomy