Cystodium is a fern genus in its own Cystodiaceae family. It contains a single species: Cystodium sorbifolium (Sm.) J.Sm. 1841. Because it looks like a small tree fern, it had previously been placed in the tree fern family Dicksoniaceae. Subsequent analysis had moved it to the Lindsaeaceae, but the most recent phylogenetic studies have placed it in its own separate family, Cystodiaceae, with a sister relationship to the current Lindsaeaceae.