Secretiveness (hiding behind the bush). Protection from an unreasonable public or fear of openness. Female emotions, penchants, and desires (Merlin being seduced behind the white thornbush by Viviane). Is the bush bare or in bloom? Is something behind or inside the bush? (God was revealed to Moses in the form of a burning bush.)
Symbol of the personality of the dreamer. Hiding place.
According to Freud, the female genitalia.... Little Giant Encyclopedia
White thorn is the bush Viviane hides behind to put a spell on Merlin.
The wood of the white thorn also is used to make magical wands. Considered a holy plant in Christianity, the white thorn grows in Glastonbury in southern England and is said to have been brought there by Joseph of Arimathea. It blooms twice every year.