French sorrel (Rumex scutatus) is a low-growing perennial with large spade-shaped leaves. Leaves have a citrus flavour and can be added to salads or cooked as spinach.
Needs moist well-drained soil and sun or partial shade. Ultimate height up to 0.5m and spread up to 1.5m.
Note that sorrel is high in oxalic acid and should not be eaten by those with a sensitivity to rhubarb.