Riddle me this, Batman

Comfrey thrives in poor soil. It likes ditches and heavy clay, but it'll grow just about anywhere. So knowing this, where the heck does it get all the stuff that's in it? Here's a list:

Constituents:
Mucilage
Allantoin
Tannins
Resin
Essential oil
Pyrrolizioline alkaloids
Gum
Carotene
Glycosides
Sugars
Beta-sitosterol and steroidal saponins
Triterpenoids
Vitamin B-12
Protein
Zinc

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