Lepisorus thunbergianus, Family: Polypodiaceae, Scientific name: Lepisorus thunbergianus (Kaulfuss) Ching, Synonyms: Pleopeltis linearis (Thunberg) Moore; Pleopeltis thunbergiana Kaulfuss; Polypodium lineare Thunberg; Polypodium thunbergianum (Kaulfuss) C. Christensen, Common name: (Japanese common name) noki-shinobu [shinobu hanging under the eaves (shinobu = Davallia mariesii)] (English common name) weeping fern, Distribution: Japan,Korea, China, Taiwan, Philippines The suitability of the epiphytic fern Lepisorus thunbergianus (Kaulf.) Ching, common in East and Southeast Asia, for the in situ biomonitoring of atmospheric mercury levels was investigated. L. thunbergianus is an evergreen fern with young, mature and old fronds throughout the year. Fertile mature fronds were used for the monitoring since the young fronds showed a high relative standard deviation (RSD) due to a shorter period of exposure, and the old fronds showed significantly high mercury concentrations with a slightly high RSD.