I hope you'll get more information from others than from me. I did a search on some pages since I knew nearly nothing. Here are some responses:
-the bridal wreath (Brautkranz, Jungfernkranz) is fixed to the hair of the bride
- it is in some places made out of hair
-according to a song (and you know that song lyrics are not very reliable) the herbs have to be: lavender, myrtle and thyme
- I have no idea what they mean, neither in Germany nor elsewhere.
- In other pages I have found rosemary and evergreen mentioned.
Your guess as to what Kränzelkraut could be might well be true.