On what famous fairy tale is the novel, Lady of the Trillium, based?

The novel's characters are based on the Rapunzel tale, Mikayla being taken from her parents, the king and queen, and imprisoned in Haramis' Tower, where she is trapped until she can claim her own powers and be united with her prince, her other self, here present in Fiolon. As in the story, the witch seeks to break the bond between Mikayla and Fiolon in order to preserve her hegemony, a self-destructive which has become a debilitating, life-threatening disease, until she is able, through selfsacrifice, to achieve immortality through her successor, Mikayla. Uzun, the harp-counselor who befriends the children, is likewise liberated from the inanimate shape into which he has been transformed.