Rhubarb — Rheum is a genus of perennial plants that grow from thick short rhizomes. The genus is in the family Polygonaceae, and includes the vegetable rhubarb (Rheum rhabarbarum or Rheum x hybridum). The plants have large leaves that are somewhat triangular shaped with long fleshy petioles. The flowers are small, greenish-white to rose-red, and borne in large compound leafy inflorescences. A number of varieties of rhubarb have been domesticated both as medicinal plants and for human consumption. While the leaves are toxic, the stems are used in pies and other foods for their tart flavor.
The genus is represented by about 60 extant species. Among species found in the wild, those most commonly used in cooking are the Garden Rhubarb (R. rhabarbarum) and R. rhaponticum, which, though a true rhubarb, bears the common name False Rhubarb. The many varieties of cultivated rhubarb more usually grown for eating are recognised as Rheum x hybridum in the Royal Horticultural Societies list of recognised plant names. The drug rheum is prepared from the rhizomes and roots of another species, R. officinale or Medicinal Rhubarb. This species is also native to Asia, as is the Turkey Rhubarb (R. palmatum). Another species, the Sikkim Rhubarb (R. nobile), is limited to the Himalayas.
Rheum species are herbaceous perennials with hermaphrodite flowers, consisting of a colored perianth, composed of six to nine segments, arranged in two rows. The flowers have nine stamina inserted on the torus at the base of the peranthium, they are free or subconnatent at their base. The ovary is simple and triangular shaped with three styles. The fruits are a three-sided caryupsis with winged sides, the seeds are albuminous and have straight embryos.
The plant is indigenous to Asia, and many suggest that it was often used by the Mongolians; particularly, the Tatars tribes of the Gobi. The plant has grown wild along the banks of the Volga for centuries; it may have been brought there by Eurasian tribes, such as the Scythians, Huns, Magyars or Mongols. Varieties of rhubarb have a long history as medicinal plants in traditional Chinese medicine, but the use of rhubarb as food is a relatively recent innovation, first recorded in 17th century England, after affordable sugar became available to common people.
Rhubarb is now grown in many areas, primarily for its fleshy petioles, commonly known as rhubarb sticks or stalks. In temperate climates rhubarb is one of the first food plants to be ready for harvest, usually in mid to late Spring (April/May in the Northern Hemisphere, October/November in the Southern). The petioles can be cooked in a variety of ways. Stewed, they yield a tart sauce that can be eaten with sugar and other stewed fruit or used as filling for pies (see rhubarb pie), tarts, and crumbles. This common use led to the slang term for rhubarb, “pie plant”. In Germany, this slang term is also used; the common name being Rhabarber in German. Cooked with strawberries or apples as a sweetener, rhubarb makes excellent jam. It can also be used to make wine and as an ingredient in baked goods.