In Greco-Roman mythology, Leuce or Leuka ("White" or specifically "White Poplar") was the most beautiful of the nymphs and a daughter of Oceanus. Pluto fell in love with her and abducted her to the underworld. She lived out the span of her life in his realm, and when she died, the god sought consolation by creating a suitable memorial of their love: in the Elysian Fields where the pious spend their afterlife, he brought a white tree into existence. It was this tree with which Heracles crowned himself to celebrate his return from the underworld.
The two sides of the white poplar leaf Servius identifies the tree as the white poplar, the leaf of which is distinctively two-sided, one white and one dark. The double color, Servius says, made a wreath that represented the duality of the hero's labors in both the upper and the underworld. The association of white poplar leaves with Heracles is also attested by archaeological remains, such as the poplar-leaf motif carved on a statue base found in a small sanctuary to Heracles (Roman Hercules) along the Tiber river.
It has been suggested that behind the vague outlines of this tale lurks an older myth having to do with Heracles' encounter with the river deity Achelous, who had chthonic associations and whose name was the subject of speculative theological etymology among the Greeks, in this case involving acherōïs, another Greek word for "poplar." In a founding myth of the 1st century BC, Heracles is supposed to have established the Arvernian oppidum of Alesia, the name of which likely derives from the Gaulish word for poplar.
Celebrants of the Bacchic rites wore a wreath of poplar leaves to honor the chthonic aspect of Dionysus.
At Elis, white poplar was the only wood used in sacrifices to Zeus, according to Pausanias, because Heracles imported the tree and used it to burn the thigh bones of sacrificial victims at Olympia. 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.
The white poplar might be worn as a crown at athletic contests in honor of Heracles, a patron of the Olympic games. Its infernal origin made it appropriate for funeral games, which played an important role in the development of Greek athletics.
The white poplar was also sacred to Persephone, for whom Leuce seems to be a doublet, as a goddess of regeneration. Robert Graves used the myth of Leuce in developing his poetic theories of mythology. Graves, for instance, holds that the back of the poplar leaf was turned white by the sweat of Herakles. In The White Goddess, he names the white poplar as one of the "three trees of resurrection," along with alder and cypress.