both round leaves but coltsfoot is not edible, to the left is coltsfoot and on the right is common sorrel
The leaf margins are different. The Tussilago is denticulate. The Rumex is entire. Here are technical descriptions for both that might help. Tussilago farfara Rumex acetosa In the case of these two plants, one could probably just taste them. While the coltsfoot contains some toxins, it has a history of medicinal use, so a small taste seems unlikely to be too dangerous. This is of course assuming you know for sure it is one of those two.
