From The Food Encyclopedia by Jacques Rolland and Carol Sherman
Also pie plant. Rheum rhabarbarum (Latin for "barbarian rhubarb"), a hardy perennial native to Asia where it was cultivated for its medicinal, rhizomatous roots. Beginning about the 10th century, travelers slowly brought rootstalks to Russia, Turkey, then farther west; by the 1800s it was cultivated in kitchen gardens in North America and sold in markets along the eastern seaboard. The large glossy leaves are toxic, containing oxalic acid which causes symptoms ranging from digestive upset to respiratory failure, coma and death. The exceedingly tart, fibrous and thick red stalks of modern cultivars are the only part of the plant commonly eaten today, cut-up, sweetened and stewed (then served plain or as an accompaniment to custard, pudding or yogurt), mixed with a sweet fruit (such as strawberries) in jam, or used on its own in crisps, crumbles or tarts, or, most famously, in pies. In parts of Europe and the Middle East, rhubarb is usually used in savory dishes. A low-maintenance favorite for home gardeners who enjoy its long spring harvest, rhubarb is also grown commercially and greenhouse-grown stalks are available much of the year. Botanically a vegetable, rhubarb was classified as a fruit by a U.S. Customs Court in 1947 (the ruling was important because vegetables were charged a higher duty).
