Oxalis acetosella, commonly known as wood sorrel, is a delicate perennial wildflower native to Europe and parts of Asia. It is easily recognized by its trifoliate, heart-shaped leaves that fold at night and in low light, a movement known as nyctinasty. The species name acetosella refers to its sharp, lemony taste, caused by oxalic acid, which made it a traditional woodland nibble and a source of vitamin C. In folklore, wood sorrel was associated with luck and protection, and it is sometimes thought to have inspired the shamrock symbol.