On the  earth ,some species with particularly high levels of oxalic acid are called sorrels (including sheep's sorrel, Rumex acetosella, common sorrel, Rumex acetosa, and French sorrel, Rumex scutatus), and some of these are grown as leaf vegetables or garden herbs for their acidic taste. 
BITTER DOCK 
 dock leaves are not edible to eat.
There are several sources of food in this family of plants. This article deals predominantly with Rumex crispus; Curly Dock, and R. obtusifolius; Bitter Dock. Not including burdock, which is not in the Rumex family.although sheep sorrel is indeed edible and delicious.but you should be careful selecting these  dock