Rhubarb is officially classified as a vegetable as it is the stem of the rhubarb plant. Like celery stalks, stems are vegetables. As a vegetable, rhubarb is far from sweet so more sugar is needed than in the average pie or you'd be puckering with every bite. But we treat these rhubarb stems, which range from green to red in color, as a fruit as it's used in recipes for pies, tarts, cakes, muffins, and even ice cream toppings. And please note that only the stems are edible as the rest of the plant is poisonous. They contain oxalic acid and other toxic substances. I got a lot of grief when I posted my rhubarb muffins with some of the stems and leaves in the background. Mind you, I wasn't suggesting you eat them raw or cooked!