http://www.vegetariat.com/2015/12/plant-guild-5-mining-plants/
Now for a little comfrey prosthelytizing: Comfrey keeps coming back when chopped, so it is often grown around fruit producing trees to be chopped and dropped as a main fertilizer. Its leaves are so high in nutrition that they are a compost activator, an excellent hen and livestock food (dried it has 26% protein), and have been heavily used in traditional medicine. Also called Knitbone, the roots contain allantoin, a substance also found in mother’s milk, which among other benefits helps heal bone