Applied to organisms that have survived while other related ones have become extinct. Often the term refers to species that have survived periods of unfavourable conditions (e.g. glacial periods or land submergence) by existing in regions called refugia, while becoming extinct elsewhere (e.g. some arctic-alpine plants). It may also refer to a surviving species of a group, the other species of which have become extinct (e.g. coelacanth fish). See also relict sediment.