Maybe there is no plant called Kraenzelkraut - doesn't it just mean "flowers/plants for your bridal wreath", whatever they may be?
As I recall Kraut is often used to mean "herb". Would A German bridal wreath traditionally contain herbs like rosemary, thyme etc? Do these herbs have the same sort of meaning that they do in English folksong? And would she wear the wreath on her head or carry it in front of her?