There are some fairly complicated nomenclatural and taxonomic issues around this genus. Whether Postia, Oligoporus, or Spongiporus is correct for a particular group of species depends on several issues. See Oligoporus for further discussion.
Spirin WA, Zmitrovich IV, Wasser SP. 2006. Oligoporus balsameus: rare Eurasian species plus notes on some related taxa. Mycotaxon 97:73–82.