Crepidiastrum platyphyllum, commonly called wadan (ワダン), is a species of flowering plant in the aster family. It is native to South Korea and Japan. It is the northernmost member of its genus. In Japan, it is found along the Pacific Coast in the Chiba, Kanagawa, and Shizouka prefectures, and in Tokyo. Its natural habitat is on rocky or sandy seashores, where it is adapted for dry, sunny conditions.