The Germans call it Rapunzel.
Rampion. Campanula rapunculus: an old European cultigen with a beautiful, star-shaped purple flower, whose leaves can be cooked or eaten raw like spinach; its parsnip-like white roots are likewise cooked or served in salads.
You know the story. The couple long for a child; finally she gets pregnant, but craves a salad made from the beautiful rampion that grows in the garden of the witch next door. (What is it about witches and gardens?)
Twice the husband manages to steal rampion undetected, but the third time the witch catches him. In the end, she lets him off with all the rampion he wants, but on one condition: she gets the child.
In due course, the longed-for daughter is born. They name her—of course—Rampion.
And once she's weaned, she goes to the witch.
No one seems to wonder why the witch wants the child. (A weanling is too big and tough to eat.) But the reason seems clear enough. The witch has no daughter of her own. What she's looking for is an apprentice, a successor.