CloudOfEarlyAutumn guessed correctly! The herb was Raspberry Leaves! An herb I've never heard of. Anyways, here's the next riddle:

I am mostly unused,
I can extract some poisons and heal most wounds.
I grow in cool places and in gardens,
And a leader showed me to an apprentice in the mountains.

I have only heard of this herb once. But thankfully, I don't have to guess. Good Luck!
~Night