comfrey!
Plant it in a place you want it, it grows well almost anywhere, but likes sun. Propagates by root division, so you just about can't "dig it out", trying only spreads it! ;-)
It has almost zero"hard to break down" cellulose it's self, but it's a compost heap innoculant. Thrives on "waste" of all types. Useful for animal fodder, but we humans may be advised to avoid it (jury is not out)
Folk named "knit bone" for it's healing properties when applied as a poultice.
There are multiple beds all around my property, I harvest whenever the plants begin to flower by cutting 95% of stems at ground level.
The leafy material gets mixed into the compost pile and soon turns "mushy" (if it doesn't start growing! ;-)
Great stuff, High in Nitrogen. A good plant in every way , (depending on your attitude towards alkaloids.)