I don't mean to post anything contraversial, but there is an almost 100% correlation between the medical uses of herbs, and magical uses of herbs.
Probably the best definition of magic I've come accross is 'change of reality by use of the will'. All the stuff that is used by magiciand, or witches or whatever are 'props' which activate the unconscious of the worker, so they can do their thing.
Here is just a start:
Salt, absolutely the most potent remover of evil, barrier to evil, it's crosscultural, everyone uses it and has used it for centuries. What am I doing right now? a Salt water flush so I can detox bromine and tolerate my pitiful low dose of iodine (6 and 1/2 mgs. that's plenty for me now).
Burdock root, used to dispell evil, it's a big ingredient in essiac tea, which I'm drinking to correct all the problems I've had with parasites.
Passionflower, it's a wonderful anti-anxiety herb. It looks like a mandala, magically it would be used to connect to divinity.
Get rid of a problem, bury a potatoe. (want to absorb toxins, eat one)
Want to create change for the better, use an apple. (the inside looks like a five pointed star, lots to work with there.) I could go on and on. Ok, apples are good for you, malic acid softens gall stones. and so on.
These are just three examaples off the top of my head, and I suspect there are many more. I am begining to wonder how much of the lost western herbal medical tradtion may have survived in the few witch families who made it through the inquisition. I know a couple, they go to MD's like the rest of us, and they are just as sick as the rest of us, instead of using their herbals to cast spells, they'd be better off if they drank the stuff.
In magic, rather than being called 'law of similarities' you get to memorize tables of correspondences. I've been interested in the occult for years, because I had a triggering event as a teen that triggered an rather minor psychic ability. It may be monor, but it's been an unmistakable thread in my life, and it's very interesting to see it turn up here.