Wood sorrel is the tart, clover-leaved green of the genus Oxalis, a shamrock-shaped forage plant eaten raw the world over for its clean, sharp, lemony sourness. Each leaf is a trio of heart-shaped leaflets that fold down at night and in bright sun, carried on slender stalks above small five-petalled flowers of white, pink or yellow. Despite the shared name and matching acid tang it is not the true sorrel of the dock family (Rumex) but an unrelated plant whose sourness comes from oxalic acid — the acid it is literally named for. The whole tender plant is used raw: strewn through green salads, laid over fish and delicate dishes as a bright garnish, muddled into cool summer drinks, or pounded into a sharp green sauce, where a few leaves bring the same lift a squeeze of lemon would.