Rhubarb: The Tart Vegetable Eaten as a Fruit
{{Rhubarb}} is the edible leaf stalk of plants in the genus Rheum — botanically a vegetable, culinarily a fruit — prized for its tartness and notable for poisonous leaves high in {{oxalic acid}}.
Rhubarb refers to the fleshy, edible leaf stalks (petioles) of species and hybrids of the genus Rheum in the family Polygonaceae. Only the stalks are eaten; the large triangular leaves are poisonous because they contain oxalic acid, a nephrotoxin. The stalks hold roughly 0.2% oxalic acid (about a tenth of their total acidity), while the leaves contain about 0.5%. Rhubarb stalks have a strong, tart taste. The tartness comes mainly from malic acid, which makes up most of the stalk's 2-2.5% acidity. Raw rhubarb is about 94% water, with little nutritional content beyond vitamin K and potassium — the very high water content is why baked rhubarb dishes turn soggy unless the fruit is drained or its juice is managed. Though botanically a vegetable, rhubarb is used culinarily like a fruit, most commonly cooked with sugar in pies, crumbles, and other desserts, and also stewed, pickled, or made into jams and beverages. Its use as food is a relatively recent innovation, first recorded in 18th- to 19th-century England after affordable sugar became widely available — sugar being essential to make its tartness palatable.