: any of several plants of the genus Rheum having large leaves with thick succulent petioles often used as food
: the dried rhizome and roots of any of several rhubarbs (especially Rheum officinale and R. palmatum) grown in China and Tibet and used as a purgative and stomachic
Rhubarb (Rheum rhaponticum)—Derek Fell
Any of several species of the genus Rheum (family Polygonaceae), especially R. rhaponticum (or R. rhabarbarum), a hardy perennial grown for its large, succulent, edible leafstalks. Rhubarb is best adapted to the cooler parts of the temperate zones. The fleshy, tart, and highly acid leafstalks are used in pies, compotes and preserves, and sometimes as the base of a wine or an aperitif. The roots withstand cold well. The huge leaves that unfold in early spring are toxic to cattle and humans; later in the season a large central flower stalk may bear numerous small, greenish-white flowers and angular, winged fruits. Rhubarb root has long been considered to have cathartic and purgative properties.