Parsley

Sold by the ounce
 
Parsley is very rich in vitamin C and other antioxidants. As such it is great for reducing the risk of diabetes, treatment of UTIs, kidney stones, high blood pressure, and minor cold/flu-like symptoms. Great for any blood flow-related issues. 
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This herb is great for relationships as it can promote longevity and lust. It's popular in love spells for this reason. A more unique use is for communication with spirits and other death-related magical uses. With its connection to the dead, it is also good for protection and purification.