 The oak is the customary sacred tree of Zeus, and the substitution among the Eleans may simply reflect the more widespread growth habit of the poplar there.The hero was supposed to have discovered the tree growing on the banks of the upperworld Acheron in Thesprotia.Pausanias says this is the reason for the Homeric epithet "Acherōïda" for the white poplar, which was also called "leukē" in Greek.