This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Leuce (Greek)
Leuce was an Okeanid-nymph abducted to Elysion (Elysium) by the god Haides where she was transformed into a white poplar tree. Her story was probably connected with the white poplars which grew on the banks of the river Akheron (Acheron) in Thesprotia, a region famed for its necromantic oracle of Haides.
Very little is known about her other than Zeus describing her as a sought-out nymph and that she had agreed to be Hades' wife and queen despite never meeting him before, hinting her interest more in status and power then love. 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.