St John's Wort

Where: France, in a sort of alternate fairy tale world.  For the sake of simplicity, let's just say France.

When: Eighteenth-ish century.  Again, alternate world.

Googled: "St John's Wort."  I've learned lots about the plant, but nothing else.

What is the French name for St John's wort?  It's called a lot of things (Tipton's Weed, Klamath Weed, hypericum perforatum), but everything I've found is English.  Or Latin.  My character isn't the sort to use scientific names, but I really don't want to use the English word for it.