Diplazium is a genus of the cliff fern family that specifically includes the approximately 400 known species of twinsorus ferns. The Greek root is diplazein meaning double: the indusia in this genus lie on both sides of the vein. These ferns were earlier considered part of either the Athyriaceae, Dryopteridaceae, Aspleniaceae, or Polypodiaceae families but are often recognized as belonging to their own taxonomic family. The taxonomy of the genus is difficult and poorly known, and by 2009 has never been the subject of a complete monographic study. Their distribution is pantropical, with a few species extending into temperate areas.