In rhubarb, as in sorrel, the perianth is six-lobed. Rhubarb differs from sorrel by having nine stamens and a fruit that is a three-sided winged nut; the pericarp dries out. These are tall perennials (1–2 m) with a lush rosette of large basal leaves on long petioles and a tall, almost unbranched stem. Wild species of rhubarb are found in Central Asia, Siberia, and the Caucasus.
The roots are powerful and contain glycosides, anthraquinone derivatives, and tannins. Some Central Asian species are used as rich sources of tannin raw materials. Wavy rhubarb (Rheum undulatum L.), which grows in the steppes of Eastern Siberia, could be used as a laxative. However, the Pharmacopoeia allows only cultivated Tangut rhubarb.
In addition, various rhubarb species can serve as sources of chrysophanol, a valuable antimicrobial agent for treating certain skin diseases. The petioles of garden rhubarb leaves (Rheum rhaponticum) contain vitamin C as well as malic and oxalic acids and are used as food. For this purpose, currant rhubarb (Rheum ribes L.) from Transcaucasia is the most valuable due to its vitamin content and taste qualities.