Rheum rhabarbarum

Rheum rhabarbarum, the common, or true rhubarb, is a species of rhizome-forming, herbaceous perennial in the buckwheat family that is grown for its edible leafstalks.

It, and many of the sixty or so species in the genus Rheum, are native to Russia and Central Asia, and is cultivated throughout Europe and North America for its leafstalks. R. rhabarbarum is also frequently cultivated in China, as well, for its roots for use as the Traditional Chinese medicinal herb, Dà huáng, 大黃, though, R. palmatum is the preferred or primary species for this.

Traditional European and American use of rhubarb sees the leafstalk cooked and stewed with sugar as a sweet, most famously as a tart pie filling.

Rhubarb leaves are toxic, as they contain deadly levels of oxalic acid, which precipitates out of the fluid of the blood stream as microscopic crystals that will lacerate the glomerula of the kidneys, eventually causing a person to bleed to death. While the leafstalks also contain oxalic acid, their levels are nowhere near as concentrated as the amounts seen in the leaves.

Rhubarb leafstalk has herbal functions very similar to dà huáng, i.e., as a laxative. However, rhubarb, especially when eaten stewed with sugar, is much more mild in action, and helps to harmonize the stomach.