Sorrel (Rumex acetosa), also called common sorrel, garden sorrel or spinach dock, is a leafy perennial herb grown and gathered for its arrow-shaped leaves and their bright, mouth-watering lemon-sour tang — a sharpness that comes not from citrus but from oxalic and other organic acids stored in the leaf. Long a staple of European cottage gardens and spring foraging, it is eaten raw and young in salads, blitzed into the classic French sauce that accompanies poached salmon, and simmered into soups such as the Eastern European schav, where it cooks down — collapsing almost instantly to a soft khaki purée — to lend dishes a clean, tart edge that lemon alone cannot.