Lately I've gathering Mountain Sorrel (Oxyria digyna) and adding it to my green salads. Mountain Sorrel is one of the (few) plants used in a traditional diet up here. It's red waxy flours were used to make tea and the leaves eaten.
Very high in Vitamin C, it's leaves are crisp and have quite a tart flavour to them. Although they are high in "C" the addition of it to the inuit diet did not add the bulk of their vitamins. By far most of the vitamins in a traditional diet come from the consumption of raw meats - seal, caribou, fish and muktaq.
I enjoy the tart goodness of Mountain Sorel and will often reach down a pick up a couple of leaves for refreshment. I think it adds nicely to the salads, and I only wish I had some Nasturtiums to add a peppery counterpoint to it.