Rhubarb is actually a vegetable, but is often used in food as a fruit. In the United States up until the 1940’s, it was considered a vegetable. It was reclassified as a fruit when US customs officials, baffled by the foreign food, decided it should be classified according to the way it was eaten.” Here’s Grandma’s Rhubarb Pie By Chef Jamie McFadden it’s so good.