Caltha palustris
Early spring greens and buds of "Caltha palustris" are edible when cooked (but are poisonous when raw). Young leaves or buds should be submerged a few times in fresh boiling water until barely tender, cut into bite-sized pieces, lightly salted, and served with melted butter and vinegar. Very young flowerbuds have been prepared like capers and used as a spice.