Sorrel is a type of herb. It is most commonly cultivated as a perennial herb and its heartiness, rough texture and rich green color immediately make you think of spinach. This herb is rustic and rugged to the naked eye but can also be very delicate to the palate when served alongside fish, poultry and meats. Like rhubarb, the leaves contain trace amounts of oxalic acid, and this chemical accounts for sorrel’s tangy taste.