Also known as purple shamrock, purple oxalis is an edible plant related to sorrel, of which these are the flowers. It has a high concentration of oxalic acid, which gives it a tangy sour taste with citrus overtones. The leaves that grow on this plant are deep purple and triangular in shape. Its delicate purple flowers carry the same tangy taste as its leaves. Unlike most other herbs, purple oxalis is a plant that grows from a rhizome rather than a seed.