Welsh: "Flower Aspect" i.e. Flower Face
1. Created by Gwydion and Math ap Mathonwy out of flowers, she was intended to be the wife of Lleu Llaw Gyffes; however, forced into this marriage, she took as a lover Gronwy, a local lord, and gave him the secret of how to slay Lleu. After this, however, she fled from Caer Dathyl and took her ladies in waiting with her; the women fell into a local lake, giving it the name "The Lake of the Maidens." Being immortal, as bozon says, Blodeuwedd was instead changed into an owl.
The figure of Blodeuwedd was also used in Alan Gardner's The Owl Service.
It is thought that she represents either the deadly lover--like Delilah--and a vegetative deity who causes the death of the sun god.
She is mentioned in early Welsh literature in The Mabinogion story "Math fab Mathonwy;" it is thought that portions of Taliesin's poem "Cad Goddeu" also refers to her.
2. The wife of John Rowland in The Silver on the Tree in The Dark is Rising series. She is a member of the Dark, and though at first seems an ally, is actually trying to destroy the Old One's plans.