Dock, curled or yellow dock, swamp dock and several others are edible.  Taste is personal.  they run from bitter to sour. I do not care for these plants but they have both food and medicine value. to see yellow dock, or curly dock, the best of these edibles click next: (More) 
Caution:  Restrict the amount of dock leaves you eat because of the high tannin content and oxalic acid content.  These chemicals may be harmful to the kidneys when eating in excess. (See more)

Seeds are food for birds and people too.  But tough husk must be removed.  Starchy, bland.  Grind to flour and use in dishes require starch as a thickener.

Great Water dock, Rumex orbiculatus Gray,  

Medicine: Potowatami used the roots of this plant as a blood purifier.  Woodland Cree prepared plant in decoction (whole plant) and wash was applied to painful joints.

Meskwaki may have used the plant as a poison antidote, prepared in decoction and consumed.

 

Jim Meuninck harvesting seeds from Greater Water Dock, Rumex orbiculatus Gray.  Grows to 12 feet high. (More)